Some of the users on my forum are experiencing problems when uploading attachments. They are uploading some Microsoft word, excel or powerpoint documents. They only have a problem with some files not all.

One user tried to upload "Customer Account Plan.pptx" when he pressed upload nothing happened. The file was only 660 KB.

We tried to rename the file to "Customer Account Plan1.pptx", then it could upload.

On some files renaming does not work.

Do anyone have an idea on what the problem is and how it can be solved?

Try to gather more info, so far it looks like a regexp problem.