How to fix an approval group not working correctly
If you are having trouble approving an invoice, for example, the approve button is grayed out when it is your turn to approve, then the approval chain may have been broken. To fix this you will need to reset the approval group. Click the 'Approval Group' drop down shown below.
Then you must select the blank approval group and hit save.
After that all you do is re-select your original approval group and hit save. This will reset the chain of approval and fix the approval button being grayed out.