Did you run the Load DWH job in Full Mode after deleting the old attribute?
The problem that you are getting seems like the column still exists for the old attribute in the DWH schema. If you would have run the Load DWH job in full mode, after deleting the old attribute, you should have not got that problem, this is what I believe.
In case you have not done that, then I would say try running the Load DWH job in full mode and see if you are still getting the same problem. If yes, then delete the newly created attribute, and run the load DWH job in full mode. This will remove the column from the DWH schema. Once that is completed successfully, you can create an attribute with the desired datatype and run the Load DWH in full mode.
Hope that helps.