package Doc::User;
use base 'Doc::DBI';

__PACKAGE__->table('users');
__PACKAGE__->columns(All => qw/uid email employee/);
__PACKAGE__->has_many(accessrights => 'Doc::AccessRight');
__PACKAGE__->autoupdate(1);

1;
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Try adding an explicit

use Doc::DBI;
[download]

before your 'use base'. If I remember correctly some perl/base versions just modified @ISA with 'use base', while newer ones actually use'd it when it wasn't loaded yet.
Your mod_perl was probably compiled with an older perl version than the command line version you're running. If so, you'll want to fix that or the version difference will pop up on a regular basis to bite your rearend...

That did not help either. I am now asking the sysadmin to change the perl executable to the same i am using on the command line. Although both are 5.6.1