Concentric cell problem (Alcatel)

Dear all!
Dear Pix!
Please, help: for the first time in our network we’ve created concentric cells (multiband cells, 900 outer and 1800 inner). We’ve reconfigured 2 BTSs: one BTS900 and one BTS1800, now they are linked with a synchronization cable (1800 BTS as slave) and we have three multiband cells. But we faced the problem that a call can’t be established through this BTS (any of its three cells) at all.
Through L3 messages (from TEMS log) we can see that Immediate Assignment procedure and Ciphering negotiations were successful – MS camped on SDCCH and was waiting for TCH Assignment command but it didn’t come so we got “blocked call” (in TEMS terms). All our call attempts on each of those cells ended in similar (identical) way: calls weren’t established because the timer for waiting a TCH assignment_complete (MSC timer) had been expired. But looking on BSS counters for those very cells (just when the drive test was making) I see very interesting thing: MC140a is around 200 per hour but MC703 and MC140b are equal to 0!! As I understand it means that TCH Assignment_command was sent from MSC towards BSC (and was successfully received – MC140a), then BSC had to send a PHYsical CONTEXT REQuest to BTS (to query the BTS about the latest values for the distance between the MS and the BTS, the power level, or channel type) and after that BTS should sent a message PHYsical CONText CONFirm back to BSC. If everything is OK BSC has to send a CHAN_ACT command (and increment counter MC703) – but this doesn’t happen – MC703 is equal to 0!!!! So we must have problem with PHYsical CONTEXT REQuest/CONFirm – obviously, something like that BTS can’t transmit requested information…

My questions are:
What could be a reason for such problem? Could it be because of wrong setting for multiband cell? Or is it real HW/SW problem?

Sometimes I meet similar problem even for single cell, and they can be solved easily by recreation of RSL or BTS in OMC-R. Remembering about this experience, I’ve already recreated this multiband BTS (main and slave) in OMC-R (and locally too) but nothing has changed.

Many many thanks in advance!!!