"Content cannot be displayed" on the Lead or Account layout

Issue

The end user expects to see and use Matchmaker on the Lead page, but instead sees the following error:

"Content cannot be displayed: You do not have sufficient privileges to access the page: /apex/fcmm__LAM_MatchedAccounts"

Or this error on the Account page:

"Content cannot be displayed: You do not have sufficient privileges to access the page: /apex/fcmm__LAM_MatchedLeads"

Solutions

This user has not been granted the required permission set to see the Matchmaker Visualforce.

As described in "Step 1: Assign Permission Sets & Enable App (Required)" of the Install and Prepare documentation, there are two different permission sets: End User and Administrator. Assigning one of these permissions sets to the user will allow that user to see the Matchmaker UI.