Invalid extension(s) in list '<list>' of file type '<filetype>'
An extension listed in the Extensions property of the specified file type is not a valid file extension. Multiple extensions must be separated by semicolons; it is not necessary to prefix an extension with a period.
To correct this error
- Double-click the error in the Task List to go to the referenced file type in the File Types Editor.
- In the Properties window, select the Extensions property, and correct any invalid extensions.