Error code -2147220961 (MultiTerm 2015)

SDL MultiTerm 2015: what does the error code -2147220961 ("MultiTerm is unable to add the entry") mean? In other words, what does this mystical code tell me about the reason of such rejection? The termbase refuses to accept new entries in MultiTerm 2015 as well as in Studio 2015.

Characteristics: Termbase created by Glossary Converter from Wordfast Glossary.

Description of problem: Rejction of entry is only on 1 PC, on my other (technically identical), I can add terms. The glossary is stored on an external SDD. All other glossaries created in the same way (all from WordFast glossaries) do work on both PCs.

Perhaps the meaning of the error code can make it easier to understand what the background of this "refusal to work" might be.