Help Outlook/Meeting Invites do not have accept/deny button



I have a user at work using Samsung Moment (SPH-M900) with OS 2.1 update 1. Currently at work we use Exchange 2003 with Outlook 2003. Before when someone sent him an invite the meeting invite email appears on his Samsung/Android phone and has the option to accept or deny the meeting. However, over the past few days when he receives an a meeting invite it appears as regular email on his Samsung/Android phone and no longer gives the Accept/Deny button.

Can anyone offer any assistance in this issue?