I have a saved search where results are grouped by document numbers, on clicking the grouped document number link in the saved search, I am getting the following error:

An unexpected error has occurred. Please click here to notify support and provide your contact information.

Is it an issue with the saved search or the system?

it's an issue with the saved search, either you got field that has invalid value or the field itself is invalid. but in order to figure out which one it is you will need to open support case unless you know which field might be the cultprit

I figured it out! I was grouping Customers in the saved search, but I was using the wrong Customer fields.

that message "`An unexpected error has occurred. Please click here to notify support and provide your contact information`." I just ignore. If you are creating a saved search and you get that message then just do what you did and assume you have a problem in your search. Look to your groupings or sums or formula and usually we are asking a search to do something that cannot be done.