I have installed a long time ago two 1750 routers and one 2610, that had serial connections. Then, my costumer started evolving his network and wanted to put up VoIP. At the time, the available IOS was 12.0(7)T and the config was based on multilink interfaces.
Meanwhile, the same costumer became interested in V3PN, but realized that the existing routers, though old and now unsupported, fitted his purposes with VoIP over IPSec over ADSL. After recommending the routers replacement and being ignored, I started the tortuous process of implementing a WIC-1ADSL on the 1750 routers and implementing IPSec. The tunnels are up and running and the data packets flow without problems. As anyone can imagine, it was a headache to find an appropriate IOS - 12.2(8)TPC10b - the latest one available to the 1750 routers.
After the implementation of IPSec and data flow, I removed the serial interfaces and it was time to put the voice up to work with the IPSec tunnels, because it was already working with the serial interface before, which was merely (I thought, after being surprised the ADSL an IPSec worked fine) a question of sending voice packets over the IPSec, with the best QoS possible.
From the way from the 2610 router to the 1750 routers, I can establish a h.323 voice session and talk normally. From the 1750 #1 to the 1750 #2 and from these to the 2610, I can't even connect a session, it fails, I believe on the Hook Up event, or at least on the number dial. The 2610 has an ASA5510 making the Internet border, but the data flow is ok, and the ACLs that define the encrypted traffic are working nicelly.
I really can't see what the problem is.