This error:
Can't open table. Invalid INT file index definition. Index does not exist on server, OR this is an incomplete client index definition.
usually means there is an index mentioned in the INT file, where that index does not exist on the SQL backend.

For example:
Removed the index Vendor002 in SQL Studio, but my Vendor.INT still has this reference:
INDEX_NAME Vendor002
This table can no longer be opened, because the index definition can no longer be obtained. In DataFlex versions before 19.0 you could open such table, but the index would be unusable and when used could cause unpredictable results.

To resolve from this situation you can do a Repair with the SQL Connect/Repair wizard. This will remove the index definition from the INT file. Note the index must be re-added after this.