I'll supply a few links about forms at the end, but this is a good example why we at the office felt forms were dead on arrival. They can require that Outlook be the same version and that VBA, VB runtimes be installed and enabled. Some privacy software such as McAffee or others can thwart forms as well.

To recap, the creator of the form may have all that is needed enabled on their machine but then needs to enable the same on each machine they want the form to function. After a few weeks of this we decided to dump forms and go back to other methods.

Light reading:

http://support.microsoft.com/?kbid=146636
http://www.slipstick.com/addins/mssampleapps.htm
http://support.microsoft.com/?kbid=290655