If you haven't tried Arun's suggestion, here is another solution you can try. The benefit of this method is, you don't need to uninstall STAAD.Pro.
It is advisable to ask the IT person in your office or someone with administrator rights to your computer to do this. It should be done before you run STAAD.Pro.
Go to Start menu ->click Run-> type REGEDIT, click “OK”.
The Registry Editor window will appear. Expand HKEY_CURRENT_USER-->Software-->Research Engineers-->StaadPro. Under that, you will find a key named 2007. Delete it.
Exit the registry editor.
Start the program again and see if it works.