This does not happen every time but is consistent enough that you should be able to recreate it. I have recreated it three times. These are the steps:
1. Check out a book for a patron, or find a patron that has a book checked out already.
2. Go to User Information for that patron and add a Patron Block that blocks Renewing.
3. Go to Open Loans and attempt to renew the loaned item.
4. A pop-up will occur (like what is shown in attached screen print renewing-with-block.JPG) that provides a Block Details button.
5. Click on the Block Details button.
6. You will be sent to the User Information page, where a system error will pop-up (like what is shown in attached screen print block-details-button.JPG).
7. If you don't get the error, try renewing again. Close Chrome and reopen it. It will happen.