Sounds like you have damaged your file and this is likely due to the way your are sharing your file over the network.
If two users attempt to access the file directly on the shared directory at the same time, you can get a corrupted file. Also, having the first user host the file from a shared directory has an increased risk of damage to the file if he gets a network "glitch" while he has the file open.
FileMaker Techs recommend that you always host the file with FileMaker Pro by first opening it with FileMaker Pro on the computer where the file is located, then other users use open remote to connect to the file. The file should not be placed in a shared directory to prevent uers from attempting to open the file directly over the network.
Recover the file and test the recovered copy to see if it works.
Things to keep in mind about Recover:
- Recover does not detect all problems
- Recover doesn't always fix all problems correctly
- Best Practice is to never put a recovered copy back into regular use or development. Instead, replace the damaged file with an undamaged back up copy if this is at all possible. You may have to save a clone of the back up copy and import all data from your recovered copy to get a working copy with the most up to date information possible.