Import failed. Unable to find value map index

Hallo all,

I have some problems with data import using Import Manager. I want to import product information and created a mapping for XML files. I already successfully loaded several hundred records but now I have some files which I just can't import: The mapping seems fine, at least, it allows me to start the import mechanism. but suddenly, the "Import records" step fails and the log tells me something about an "Import failed. Unable to find value map index" error. This is really confusing since I can't see where the problem really is and what this means. Does anyone have an idea where I can start looking?

I am using MDM 5.5 SP5 (5.5.42.xx).

Thanks and best regards,

Martin