Run Data Integrity Check and see if it will fix the error using Rebuild. Odds are it won't but it's a first try.
If that fails, yes, you will have to restore from a backup. Just the GL data unless you have retrieved from subledgers since the last backup.
If you have retrieved from subledgers, or if your backup is really old, another option is to get the data repaired - ask your consultant about how to do that.
There is another possibility which is too complicated to mention here - have your consultant contact me if he/she is interested in it.
Steve