I recently had the dubious pleasure of debugging a User 42 Panic on a piece of Symbian code that was given to me by another company. You always need to make sure you understand what the system is telling you, so I went straight to the documentation:

User 42: This panic is raised by a number of RHeap member functions, AllocLen(), Free(), FreeZ(), ReAlloc(), ReAllocL(), Adjust() and AdjustL() when a pointer passed to these functions does not point to a valid cell.

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