Navigator uses indexes to keep track of accounts. Sounds like the indexes may be corrupted.
Do a Software Update. There is a newer version of Navigator 8.2 available. It is good practice to do a Software Update every month or two. The update will tell you if a new version is available.

If that doesn't fix it, try rebuilding indexes:

1. Back up your data.
2. Select Tools | Test and Correct | All of the Above. We are interested in Account Alphabetical Indexs and Chart of Accounts Index, but might as well do them all.
3. Note any problems that are reported when Test & Correct runs.
4. Check to see if the problems are fixed.

If that doesn't fix it, you can rebuild the Account Index:

2. Back up your data.
3. Select Help | About Financial Navigator.
4. Type "t" on your keyboard. "Set to test mode" appears.
5. Select OK twice.
6. Select Tools | Test and Correct | Rebuild Account Index.
7. Note any problems that are reported when Test & Correct runs.
8. Check to see if the problems are fixed.

Note that there is also an option to Rebuild Chart of Accounts. That is only a last resort, because when you do that all you Category names will revert to default and you will loose any customized names. If you think you need to do this, ask for instructions first.