How to add file type to the list of mimetypes allowed in issue reports

I've got a private Redmine installation - 1.0-stable.

When I update an issue and try to attach a .png file, I get an error:

"Application error
Rails application failed to start properly"

Other file types (pdf, doc, etc) work well.

Do I need to add .png to the list of allowed file types? If so, where do I do that?

Thanks in advance.

- Muyi

Redmine