I encountered a rather odd error the other day when I was having to do schema changes between organizations that involved a lot of importing and exporting when at one point I could not import the solution into one of my target orgs anymore.
After some digging through the Dynamics logs, the problem became very clear.
I had a field that had been incorrectly typed, so in my source org, I deleted it and recreated it. When I proceeded to import the solution updates into my target org I could not perform the import because the field already existed but in an incompatible field type.
Specifically, doing some searching through very verbose CRM log file yielded the following entry.
Attribute new_legacyid is a Integer, but a String type was specified.
To get around this issue, I removed and deleted the field new_legacyid from my target org and then performed the import again, which then went smoothly from there.