Hi Michael,
I saw the same error when compiling XOTcl 1.4 against Tcl 8.5 from cvs head, where TclIncrVar2 is commented out in the internal stubs table for tclIntDecls.h. (on SUSE 10.1 x86-64)
At least there is a patch here: http://alice.wu-wien.ac.at/pipermail/xotcl/2006-April/005074.html
Bernd.