PC freezes when opening attachment

Hello

We have SEP (version 12.1.4013.4013) running on our Windows 8 pc's.

Now when we open an attachment in Outlook 2013 (for example a 1MB jpg) the PC freezes (100% Disk) for a couple of minutes before the attachment is opened.

When we disable SEP the attachment is opened immediately without any problems.

Any idea how we can fix this?

Best regards

Jef