Unable to Enter Exchange Rate in a Transaction from a Custom Role

The role needs to have Currency Permission with at least an Edit Access Level.

 

Steps to modify the role setting:
1. Login as Administrator.
2. Navigate to Setup > Users/Roles > Manage Roles.
3. Edit the custom role.
4. In the Permissions tab > Lists subtab > Look for Currency Permission, if it's not listed, add the permission and set the level to Edit.
5. Click Save.