This issue seems to be related with the field types in your base view. Could you please remove the additional field type properties from the two columns?
To do this, in the VDP Admin Tool, go to the base view, click on "Edit", and click on the "Edit field type properties" button next to the field type. On the dialog that pops up, delete the value in the second box ("Type size"), and click "Ok". Do this for the two columns, and then click on "Ok" to save the changes on the base view. Now, invalidate the cache contents and try again.
If you're still having this issue, could you please share the VQL of both your datasource and your base view? (Remember to remove all the information about the URL, user and password from the datasource VQL before posting)
Hope this helps!