I ran into the same issue when running a project locally, after the datatype of an attribute was changed in an external entity. Design time in the modeller it showed that the datatype was changed and Mendix asked me to update the information. Then when running the project still an error pops up: An error occurred while initializing the Runtime: Change of data type or length for key attribute 'xyz’ is not supported in external entity key for entity 'abc’.
The fix is rather stupid in my opinion and Mendix needs to fix this:
This is very helpful! Thank you!
The solution(hack) that worked for me was to delete all the entities and constants that came with the datahub and re-added everything afresh again.