Hi,
Looks like either the syntax for instantiating multi_usrp has changed (seems unlikely), or a bug was introduced, likely in 7/2-7/4's recent gr-uhd refactoring (1eaa96b, 350d285, fe58537, 3c42e79, 691bdaa). Sorry I haven't gotten more specific than that. The attached flowgraph, when used with a USRP1 (yes, I know, I'm probably the only guy using one) returns:
RuntimeError: LookupError: IndexError: multi_usrp: TX channel 1 out of range for configured TX frontends
Prior to the above commits the error does not occur.
Best,
Nick
uhdbug.grc