Strange error with WEKA Classifier inside a loop - says "Cannot handle STRING Class", outside the loop it can handle...

I have experienced a strange problem, in one place in the graph I can train WEKA IBk classifier with exactly same data structure, but inside the loop it says it does not support string class. Anyone have any idea what can be wrong? Data for nodes 43 and 44 is exactly the same (same cell values, same rows count and IDs, same columns count, names and types).

It looks like that after the Split Collection node the domain is incomplete, if you apply the Domain Calculator (instead the Column Rename) the node works, I agree the error message is missleading.

For additional clarity, the problem is that the split collection column does add a table spec for the columns that it generates while the FIle Reader does.  Adding a domain calculator after a split collection column will be necesarry.