The problem is that although you type precisely gpedit.msc, Windows 7 cannot find gpedit.msc. The most likely cause is that you have the Home Premium edition. It's most disappointing that you only get gpedit.msc in the Ultimate, Professional (old Business) and Enterprise editions, and not in the Windows 7 Home Premium or Basic editions.
Another common problem is that you forget to type the .msc file extension. Windows 7 cannot find gpedit unless you append the .msc file extension.
Other than it could just be a plain typo, gdedit.mcs or some other anagram.