Note: Your IT will need to make changes to permissions on the SQL Server, so please pass this information to them.
On the SQL server, expand the server in the Object Explorer and then go into Security and Logins.
Double-click the account with the A on the end for both the user that it isn't working for and another user that can run the report.
Click User Mapping for both users
For the user that cannot run the report, modify the mapping for all databases and the roles assigned to match those of the other user that is working.
Click OK to save the changes
Get the user with the error to log out and back in again.
The reason for doing multiple databases is because if the report is modified, it may be using data from a different database, causing the report to still not work even if the main database permissions are identical.