Sometimes, although your mouse has been configured to work for a left handed user, when logging in to SIMS Terminal Server, the settings are lost.
If this is the case, downloading and installing the appropriate Microsoft Intellipoint driver software corrects this. In some cases, you may need to consider purchasing or locating a newer mouse compatible with this software.
Drivers are found here – http://www.microsoft.com/hardware/en-us/downloads
Select the driver according to which Microsoft mouse you use. Configure as appropriate from Start > Program Files > Microsoft Mouse settings.