During the DT, Which layer 3 messages does the MS receive ?
The HO Command ?
If no : then problem in your MSC database.
If yes : then resume reading…
Look inside this HO command :
you should see the frequency and TS of the target cell on which the MS should connect.
Are they correct ? Is it indeed the target cell towards which the MS should go ?
If yes : then it means the MS tries to connect to the right cell, but with wrong parameters.
On top of my head:
1/ problem of clock in the target cell ?
2/ problem of ciphering ? are both sides using the same ciphering mode ? (A5/1 ? A5/0 ? A5/3 ?)