Have you tried turning on DBI's tracing capabilities? DBI provides several different trace levels. You can control tracing with DBI->trace( 1-4[, "logfilename"] );. You can also trace per handle, but you won't need to do that here. By default, the trace output will go to dbitrace.log. You can also set the logfile name and trace level via the environment variable $DBI_TRACE.

DBI_TRACE value     Effect
1                   DBI->trace(1);  # legal values: 0-4
mytracefile.name    DBI->trace(2, 'mytracefile.name');
3=logfile.txt       DBI->trace(3, 'logfile.txt');

Trace Levels        Effect
0                   Off
1                   Trace method execution inc returned values and errors
2                   1 + method entry & parameters
3                   2 + more internal trace info
4                   3 + the kitchen sink