In certain cases, when printing to Print2Email through Citrix XenApp web interface and trying to send an email, the following error message could appear:

This error occurs, when using MAPI (Outlook) for email sending in Print2Email, and the Outlook is actually opened on the system, at the current user.

The running Outlook prevents Print2Email to send the email due to permission issues. To resolve the problem, close the running Outlook at the current user, and try to send an email with Print2Email through Citrix XenApp web interface again.