Hi Guys,
The 1.9 version of this plugin is no longer maintained.
The error message you received does not seem to be related to the certificate module, however you did state that when you delete the module it works, which I find very odd.
In developer debugging mode was there a stack trace that listed the line numbers in the files that were executed to lead to that function call? If so, please post it here and I will try and help you sort out this issue.
Regards,
Mark