I just unlocked my Storm 9550, i experienced the same thing, can not type MEP2.
It could be you typed it wrongly without knowing.
Restar again, and it will be fine as i did
Here is how to unlock
1. Press the Menu key
2. Scroll to and select Manage Connections.
Select Turn All Connections Off.
3. Press the red end key or the Escape key to go back to the Home screen.
4. Scroll to and select the Options icon.
5. Scroll to and select Advanced Options.
6. Scroll to and select SIM Card.
7. Type MEPD
Note: When typing in MEPD the letters will not appear on the screen, this step open up the personalization on the device.
8. Type MEP then hold "ALT" key and type number 2.
Note: When typing in MEP ATL 2 the letters/number will not appear on the screen, this step open up the xxx8220;Enter Network MEPxxx8221; box.
9. Enter the unlock code.
10. Press Enter , you should see "Code Accepted"
11. Press and hold power key to turn the handheld off and then back on.
12. Once the device has powered on, follow steps 1 & 2 and restore connections.