IE9 won't ask to save *.xlsx file

Hi all.
I'm having some issues with IE9 on my Windows Server 2008 R2, when users try to download an *.xlsx file, it's being opeden ini a new tab and shows some strange characters, it doesn't even asks to save the file, when they try to use "Save target as..." IE saves the file as a *.txt file and not *.xlsx why it's happening like this ?

Print Screen:


Need some advice, thank you.

Forgot to say that under Administrator account, I'm able to save the *.xlsx file and I can open it without a problem.


Only users within Users Group have this issue.

Just wanted to test downloading an *.xlsx file from another website and guess what? it's working, IE9 asks where to save the file, really can't understand what's happening, why it doesn't want to work with that specific website ?!

Tested with another random website and it's now working again...