Don't know if you noticed but the last post here was over 6 years ago. Methinks you didn't figure it out - you worked around it. Possible cause:
the data type of the bound column was not visible and that is the value you were trying to save in the table, not the value which is in another column that you saw in the combo after selection.
The error messages can seem like alien speak at times, but with experience, most of them will make perfect sense, as does that one to me. I may not have hit on the exact reason, but the cause for the error provides much to go on if you know what it means.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.