Users with Internet Explorer 8 and above will not be able to connect to CEM+ versions before 3.0.
The solution is to make internet explorer 8 pretend it is IE6 by emulating its user-agent string.
Bayden Systems has released a freeware IE8 add-on that does just that. You can find the utility at http://www.enhanceie.com/ietoys/uapick.asp
Note that there are different solutions for Internet Explorer 7 (Sensor+ Connect with Internet Explorer 7) and Internet Explorer 9 (Sensor+ Connect with Internet Explorer 9).