What is really the level check

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Hello Group,

       I have a small problem that I can not understand...

We have got a CL program running at the end of day, this program creates a
logical file from a dds stored in a source library and calls a number of
RPG programs and then it deletes the file at the end.

I understand that the RPG program opening this file can give a level check
error message when something significant in the file is changed, but
actually the Physical file structure and the logical file structure never
changed. Once I get this problem I recompiled the RPG program and I
thought that his should solve the problem. But the next time I got the
same error message again. I check the record format level identifier of
the file and the one used in the program compilation and to my surprise I
found them the same...Could you please explain to me what I am missing or
advise me what I should check else?

Thanks in advance for your help
Kind regards
Heba