First thing when facing a problem is to refresh the metadata, as the database schemas might have changed.
That process will get all the needed metadata from the source and target databases and remap all of the tables.
In most cases that will solve your problem.
Unknown data types
Some combination or data types cannot be mapped from source to target, and you can Edit the table mappings and manually set your desired type.
Also, there you can deselect the problematic column and it will not be used in the run.
If you think there is a problem with the mappings or you cannot find a way to make your table work, please contact us at firstname.lastname@example.org and we will be glad to help.