msn messenger 5.0

hello! i have an msn messenger 5.0, when i start my computer and log on to the internet the msn messenger ads says that there is an upgrade to my messenger then they ask if i want to upgrade. and i said yes. then after upgrade i tested the new msn messenger and the program would not run anymore. it says ?windows cannot access the specified device, path, or file. You may not have the appropriate permissions to access the item?. What happened???? I thought this was an upgrade, I never thought that it could ruin my messenger like that. Thanks for your help. I need it badly!!