Fatal error: Cannot instantiate non-existent class:

I have searched previous posts on this type of error and still do not quite understand what the error is. In the case of this particular error I was trying to install the rewards mod (I will be contacting the author as well as there was not a support forum). We are running 1.3.7.1 PHP 4 (something) and I am not sure of the MySQL version. I am unable to log in for that info right now due to this mod being bad and causing problems.

Please help in any way you can and I will be fixing the modded files from last friday and will log back in with additional once I get it fixed.

tia...

0be1