asterisk users - Apr 2006 - g.726 codec not working in one direction

Hi,

Iam using Asterisk Asterisk 1.2.5

Iam calling:

NOT OK: 
phone A ->ulaw -> Asterik-A -> gsm -> Asterisk-B -> g.726 ->
POTS phone B

NO sound from from phone A to phone B, phone B to phone A works

If iam using ulaw to connect from Asterisk-B to POTS phone B everythink is OK:

OK:
phone A ->ulaw -> Asterik-A -> gsm -> Asterisk-B -> ulaw
->POTS phone B

Any idea how this can happened?

If additional information required please ask..



best regards

Thomas