AVM C2 BRI card configuration on Asterisk

We are running an Asterisk @ Home PBX server with an AVM C2 BRI card with two ISDN channel. Each ISDN channel should give us two line, giving a total of four lines. However, only two lines are working. We have replaced the AVM card with a new one and the problem persists. We have also tested the ISDN lines and they are both working correctly. We need someone to resolve this configuration problem so that all four lines (both ISDN channels) are working with the PBX. We are presently running Asterisk@Home version 1.5. We are happy to consider upgrading to a more recent version is this will solve the problem.