Users with Internet Explorer 7 will not be able to connect to CEM+ if running (at least up through CEM+ version 2.1).
The solution is to make internet explorer 7 pretend it is IE6 by emulating its user-agent string.
Microsoft has a utility that does just that which should be linked from the following Microsoft knowledge base entry. http://support.microsoft.com/kb/923196/en-us
The linked download is an .msi (Microsoft installer) file. Double-click to install and then follow the prompts. Once installed, reboot and then you will have a User Agent String Utility shortcut in the program area of the start menu which will launch ie7 with the proper modifications.