This problem happens when grant numbers are assigned and the operation is cancelled.
There is an easy way to fix the issue.
Go to Tools > System Utilities > Set Automatic Numbers
Grant Number is already selected. On the right, type in a grant number that is one larger than the Last Grant Number Used value and click Done.
Note: It might be necessary to increase the number more than once. i.e. if the Last Grant number is 20170033, try 20170034, but you might need to move to 20170035 or higher.