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>To be honest, it was my error in this stored procedure, which I just fixed. However, what if NextID table could not be opened or locked? In this case this function still would return 0 and we would end with 0 as Primary Key...
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If you return NULL from your stored procedure (when an error occurs), your table should not allow the append. You need to make sure the accept NULLs box is not checked for the primary key field.