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in reply to Error ... at (eval 75) line 7974.

I hit on this old thread when I had the same problem, and later found out something not previously mentioned. Setting
$^P= 0x100;
gives you the source line of the eval itself in addition to the line within the eval:
Use of uninitialized value in print at (eval 1)[./testeval.pl:12] li +ne 1.
I found this quite useful for tracking down the offending eval'ed code. See the documentation of $^P / $PERLDB in perlvar for details.