Today I've been working on a nasty error which showed up during importing customizations. The error message was:
This attribute map is invalid. The selected attributes should be of the same type. The length of the source attribute and the formats should match. The targe attribute should not be used in another mapping."
To solve this error I have opened up the customizations.xml file and located the attribute maps ("ctrl + f" and search for AttributeMap). There were many custom build maps between exisiting entities. To find out which of these caused the error, I have removed them one by one until the error did not show up. That was the record that I needed to check and indeed that was the problem. The source entity did have this particular attribute set as a picklist and the destination entity had the type of the attribute set to bit. In the CRM system where I created the customizations file, both attributes were bits.
I hope this approach does help you solve the issue as well. Good luck!