Troubleshooting SyteLine MRP and APS regeneration that fails or hangs
SyteLine MRP regeneration fails to complete
Also searched as
- SyteLine APS scheduling engine error
- CSI MRP job stuck running never finishes
- SyteLine planning run timeout error
- SyteLine MRP net change vs regenerative failing
Short answer
A SyteLine MRP or APS run that fails to complete, hangs indefinitely, or errors partway through is most often caused by data integrity problems (a BOM loop, an item with an invalid lead time or missing routing), a scheduling engine (APS) process that is stuck or resource-starved, or a concurrent MRP run conflict. Check the MRP/APS log first for the specific item or job it stopped on before assuming it is a system capacity issue.
Applies to: SyteLine 8.x/9.x with Advanced Planning and Scheduling (APS), CloudSuite Industrial 10.x
Diagnose a failed or hung MRP/APS run
- 1Check the MRP/APS run log (Planning > Net Change/Regenerative MRP log, or the APS scheduling engine log) for the last item, job, or operation processed before the run stopped - this almost always identifies the offending record.
- 2Look specifically for BOM loop errors (a component that circularly references its own parent, directly or through several levels), which will stop or corrupt a regenerative MRP run.
- 3Check for items with missing or invalid planning data - zero or negative lead times, missing primary vendor on a purchased item, or a manufactured item with no active routing, all of which can cause the planning engine to error or produce nonsensical results.
- 4If using APS, confirm the APS scheduling engine service is actually running and was not left in a stuck state from a prior run - a hung APS process can block subsequent runs from starting cleanly.
- 5Check whether another MRP/APS run was already in progress or improperly terminated (e.g. server reboot mid-run) - SyteLine generally will not allow a second full regeneration to run cleanly while one is still marked active.
- 6Review server resources (memory, CPU, tempdb space on SQL Server) during the run window - large regenerative runs on sizeable item/BOM datasets are resource-intensive and can fail silently if SQL Server runs out of tempdb space or the app server times out.
- 7For a suspected BOM loop, run a BOM where-used/loop check report (or query bom_ items in SQL for circular parent-component chains) to find and correct the structure before rerunning MRP.
- 8After fixing the root data or resource issue, run Net Change MRP on the affected item(s) first to confirm the fix before committing to a full regenerative run.
Net change vs. regenerative failures look different
A net change MRP run that fails is usually isolated to a small set of items and their immediate BOM/routing relationships, making the log easy to interpret. A full regenerative run touches the entire item master and BOM structure, so a single bad record (a circular BOM reference, an item with corrupted planning fields) can stop the entire run partway through, and the log line where it stopped is the fastest lead to the cause.
If regenerative MRP consistently takes far longer than expected or times out (rather than erroring outright), that points more toward a resource or dataset-size problem - large multi-level BOMs, excessive obsolete items still flagged as planned, or SQL Server tempdb/memory pressure - than a single bad record.
BOM loops are the classic hard-to-spot cause
A BOM loop happens when, several levels down a bill of material, a component eventually references back to one of its own parent items, either from a data entry mistake or from reusing a phantom/subassembly incorrectly. SyteLine's planning engine cannot resolve an infinite structure and will either error out or hang. These are hard to see by browsing the BOM in the UI because the loop can be four or five levels deep - a direct SQL query or a dedicated BOM loop check report is the reliable way to find it.
-- Simplified idea: look for an item appearing as both a parent and, several levels down, a component of itself
-- (Use SyteLine's BOM Where Used report for a supported way to trace this; direct SQL should be read-only diagnostics)
SELECT item, comp_item FROM bom_ WHERE item = comp_item; -- direct self-reference, easiest case to catch
APS-specific stuck states
Because APS runs as a separate scheduling engine service rather than purely inside the SQL Server MRP job, it can get into a stuck state independent of the database - for example if the service crashed mid-calculation but SyteLine still shows a run as 'in progress'. Restarting the APS scheduling service (not just re-triggering the run from the SyteLine UI) is often required before a new run will start cleanly, and this is easy to miss if you only look at the application-level log.
Common pitfalls
- !Re-running a full regenerative MRP repeatedly without checking the log for where the previous run stopped - you will likely hit the same failure again.
- !Assuming a slow run is a 'server needs more power' problem before checking for a genuine BOM loop or a huge count of items still flagged as MRP-planned that should have been made obsolete.
- !Not restarting the APS scheduling service after a crash, leaving the system in a state where new runs silently fail to start.
- !Fixing the BOM loop but not rerunning MRP fully afterward, leaving stale planning data (safety stock recommendations, suggested orders) that reflects the broken run.
- !Running a full regenerative MRP during business hours on a large dataset, which competes for SQL Server resources with normal transaction processing and can make both slow.
How an ERP-grounded AI assistant handles this
With ERPray grounded on a company's SyteLine data, a planner can ask in plain language why last night's MRP run did not finish, and get back the specific item or BOM structure the log stopped on, cross-referenced against recent item master or BOM changes, instead of manually parsing planning logs or running ad hoc SQL to hunt for a circular BOM reference.
Frequently asked questions
How do I tell a BOM loop from a genuinely large, slow-to-plan BOM structure?
A loop causes the run to error, hang indefinitely, or produce clearly wrong results (infinite exploded quantities); a large-but-valid BOM just runs slowly and eventually completes. If a run has been active far longer than your historical baseline with no progress in the log, suspect a loop or a stuck process rather than just size.
Does a failed MRP run corrupt existing planning data?
It can leave planning data partially updated or stale if the run stopped mid-way, which is why re-running MRP (net change on the affected items, or a full regenerative run once the root cause is fixed) after resolving the issue is important, not just clearing the error.
Is APS required, or can SyteLine run MRP without it?
SyteLine supports both standard MRP and the more advanced APS scheduling engine; APS adds finite capacity scheduling and its own service process, which is a separate potential point of failure beyond standard MRP/database issues.
Can I schedule MRP runs to avoid resource contention?
Yes, most sites schedule full regenerative runs overnight and rely on net change runs during the day, specifically to avoid contention with normal transaction processing on SQL Server.
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