asterisk users - Oct 2005 - Asterisk 1.2beta and te411p: incorrectly reporting sometimes "all channels busy"

Hi,

we have strange problem on our new card. Sometimes it reports "all channels
busy", so call cannot be made (it doesn't even appear in log).

We've contacted Digium support, but received no usable answer (they've
told
us that this card should work on stable Asterisk version - AFAIK this is not 
correct)...

Any advice, what to check and what are possible cause of such behaviour ?

Thanks in advance,

regards,

Rob.