When a problem starts coming up often, it usually means it's time for a tip addressing it.

The problem:

“I want to insert an image into my signature. When I click advanced edit I then click yes on using another editor. I then get an error saying it can't find an editor for "H(.) files" . Help!”

Go to Control Panel, Internet Options, Programs tab and change the default HTML editor to another program in the list and apply. Change it back to whatever you to use as the HTML
editor.