This is specific to these (two) agents and follows them across browsers, computers, etc.

The full exception is here (taken from PerlEx, though mod_perl does the same):

Precompiler: Execute Error:
    Filename:[C:\OTRS\otrs-3.0.0\bin\cgi-bin\index.pl]
    Package:[PerlEx::Precompiler::c_::otrs::otrs2d3_0_0::bin::cgi2dbin::index_pl]
Params[]
Magic number checking on storable string failed at ..\..\lib\Storable.pm (autosplit into ..\..\lib\auto\Storable\thaw.al) line 415, at ../..//Kernel/System/Cache/FileStorable.pm line 128

PerlEx: Error return: -1

I assume this is a corrupt user preference, but I can't find one in the table that looks bad.

Any suggestions?  We're on OTRS 3.0.3.

Hugh