Error 1190 in module 19

We are running Navision 3.6 with data on SQL server 2000.

While making a Backup in the Tools section we get "Error 1190 in module 19" on a table. This error points to data data has been incorrectly inserted in the table, so that the data is incosistent with the type of the field or there are illegal characters, like spaces etc at the beginning or end of the line.

Now if I run the database test of "Database Information (Tables)" and I check all options I do NOT get an error.
I checked all the fields for errors or faulty data but could fine nothing. Navision is running fine and everything is working perfectly except for the Backup.

I exported all the data, dropped the data and re-imported it without changing a single character and the Backup works.

Is this a bug? Is there an extra check being run while running the Backup?

Thanks for your input.