Site settings - site banner - banner image type error message

[rediguana]

Just tried uploading a .jpeg banner file, and it resulted in a rather terse 'Error! o type' message. I twigged that the error was probably the .jpeg extension, changed it to .jpg and it worked fine. The error message probably needs to be a little more descriptive to identify what the problem was, and that it was associated with the image uploaded - especially as I had been modified other site settings at the same time, and it wasn't immediately clear what the Error! was related to.

[srutto]

Confirmed this in the current code base: 2.6.1
Uploading .jpeg throws the error below:

.jpg and .png file types upload successfully