This particular error is a bug. It was reported in RT #125460 and was fixed in Tcl::pTk 0.93. It was because of a missing use Text::Tabs; statement in one of its modules, but the error it gave was unusual because rather than an "Undefined subroutine" error, the reliance on AUTOLOAD by Tcl::pTk means it was mistaken for Tcl/Tk functionality, so some other error appears instead.