I am still having constant difficulties with this.
I keep getting:
Sorry, Webmail has encountered a problem.
The error message follows: Can't call method "open" on an undefined value at /var/local/www/pn_atmail/webmail/libs//Atmail/ReadMsg.pm line 269.
If you are having continued problems using Webmail or have encountered a bug, please provide details to our support team using Contact Us, including any information provided in the above error message.
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator, firstname.lastname@example.org and inform them of the time the error occurred, and anything you might have done that may have caused the error.
More information about this error may be available in the server error log.
Apache/1.3.31 Server at webmail.plus.net Port 443
when trying to open particular messages.