Problem with cutting digit during sending destination number

I have asterisk 1.2.0 with 2 E1 and some sip phones.For more than year everything was correct.But since few months I have problems with calling out through E1. For time to time I can’t phone through E1.
I spoke with my E1 provider.Providers technican sad that I send to their central destination number without last digit.I observed debug from asterisk, everything was correct.When I do restart asterisk everything is correct.Does anybody know what can be source of problem?