Dear,
It might be an authorization issue too, hit /osu53 transaction in the command box and check if there is any authorization issue.
If yes, contact the BASIS person.
Otherwise, go to SLG1 and put the ID you are using and search for error log. It can be very handy.
Kindly also check:
http://scn.sap.com/thread/187368
Best Regards,
Rajen