I don't know if this would apply to a E1 setup, our setup is a T1/D4 standard setting did not work, the switch I am connecting to is very old, I had to connect a cable directly to the dsp and configure via a CLI, I too had a similar problem, the change was "Answer to Supervision Delay" I pushed it out to "70".

(disclaimer) I am not a telco guy, and I think my local telco knows less than I do, I came up with this setting by trying everything.