Both Roderick Johnstone and Ewan O'Sullivan have reported getting "Too many blocks" errors when using xspec v11 with complicated models. MAXBLK is set to 100 in udmget.c and there is no good reason why this should be so small. I've changed this to 1000 for the next release which should solve these problems.
Note that Bryan has updated xspec/src/tcl/Makefile so that it will rebuild libxantcl* when changes are made in the libxanlib* library. I really should be building libxantcl under the xanlib tree rather than the somewhat bizarre way it is done at present under the xspec tree.