Guess? How about printing the environment instead of guessing?
I guess because the DBI environment variables are not available to me on the shared hosting!
There is a script in my cgi-bin which lists all the CGI environment variables and there is nothing helpful in there. When I connect by SSH and run perl -e 'foreach $k(keys %ENV){print "$k - $ENV{$k}\n";}' I get environment variables for SSH and for local PERL and other directories but nothing relating to DBI
So, as it is hidden from me by the server admins, I can only guess...