# 3336 Using Cached Updates Against Live Result Sets with Expression Fields Can Cause AV During Destruction

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I have found a problem with DBISAM from about v4.28b6 onwards (problem exists in b6 but not b4 – I don’t have b5).

An access violation occurs when freeing DBISAM query components if the following is true:

1. RequestLive is True
2. The query had been cached
3. The query contains an assignment which adds a constant to a string field

The access violation occurs in unit dbisamlb at procedure DeAllocMem when the form containing the query component is closed.

Use the code below to reproduce the problem:

Run the application then close the form – an AV is thrown;

Remove any of the required conditions above (RequestLive, Cached or adding constant to string field) and there is no AV thrown.