Problem:

When using Rebuild, you may get the following error: Error during sort operation: 9/007

Resolution:

The error code 9/007 is an extended file handler error code informing you that the disk space was exhausted during the build.  Rebuild uses a series of temporary files during the process, the exact number of which is determined by the complexity of the index.

The error you received is simply stating that you have run out of room on that particular drive. What you can do is use the TMPDIR environment variable to specify another location with sufficient space as the work area for temporary files.