RoboHelp 2015 Internal error

I’m using TCS 2015, trying to compile a CHM in RH.  Don’t know if it has anything to do with it, but the source FM file is in Russian. (Spanish worked OK so it would seem it’s not a Unicode issue, but maybe something about the Cyrillic characters?

All FM files in the book open without error. I’ve saved them and closed the FMs, leaving the book open in FM.

Twice now, I’ve gotten an error message during the CHM compile that something has happened and there’s info. in C:\.err.  When I say OK, RH shuts down.

The .err file says:

“Friday, December 14, 2018 10:55:46

HHA Version 4.74.8702

htmlproc.cpp(114) : Assertion
failure: (pszTmp == m_pCompiler->m_pHtmlMem->psz)”

Any ideas?