HI,
Riccardo posted ...
... turn on Access for assistive devices in the System Preferences
You have not actually said that this is On or whether it is staying On if you have to set it.
You also have not said if you have worked through the list of links in the link Greg from TextExpander posted
I use TextExpander 2.8.1 in Mountain Lion OS X 10.8.4 without any problems.
The posters here will need specific feedback as to what you are seeing to be able to help further.
I would start myself with opening Disk Utility in Applications/Utilities and Repairing Permissions.
After that I might check that I still owned the Preferences folder where the info might be held.
My Sig is posted with TextExpander.

10:09 PM Wednesday; June 5, 2013
iMac 2.5Ghz 5i 2011 (Mountain Lion 10.8.3)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
Couple of iPhones and an iPad
"Limit the Logs to the Bits above Binary Images." No, Seriously