When a user lacks the browse users and groups global permission and attempts to create a user-based search they get the following error:

"The JIRA server was contacted but has returned an error response. We are unsure of the result of this operation."

Users should either get an error that they lack permission or better, should not have the basic search options for searching on a user at all.

Either way, THIS looks like a system failure.  This error gets people calling the admin team, asking why Jira is failing.