I had the same problem, to fix it I did the following......
1. Backup BB Device.
2. wipe handset , from the BB Device.
3. reset user activation password.
4. Remove battery from BB Device leave 10 seconds.
5. go throght Enterprise activation.
6. restore BB Device.
My system is
BES 126.96.36.199 + MS Exchange 2003
BB Device 188.8.131.52