It seems that PHP 4.3.0 changed the way the fgets() function worked. The result for the class was that when reading a response from the server, the check for "\r\n" failed, because it only read the first character. This is fixed now, and doesn't require any PHP configuration changes.
If you are using this class and PHP 4.3.0, you should upgrade to this latest version, or change line 134 of OPS.php to use fread() instead of fgets().
This release also includes a patch from Jim Cottrell to set private key when environment is explicitly set.