If the UNK table, which contains field types for fields, is "incorrect" (e.g. a number field is set as text field), you can recreate it.
If I remember correctly, this is the shortest route to recreate it (you have to do this on each server that has the NSF).
Delete FT-index. Copy-style compact of the NSF. Create new FT-index.
More about the UNK Table:
http://www-10.lotus.com/ldd/46dom.nsf/0/080cb1e381148e52852567f500615448?OpenDocument
You could possibly hande this through code if you have administration rights on the server. Then you could send console commands.