Try the following (it might solve your problem)
Try
Close Excel first and On the Windows Taskbar
1) Start->Run-> "excel.exe /unregserver"(no quotes)->OK.
2) Start->Run-> "excel.exe /regserver"(no quotes)->OK.
See the space between exe and /regserver
You might have to designate a full path to excel.exe (most likely C:\Program
Files\Microsoft Office\Office12)
In that case Start->Run "C:\Program Files\Microsoft
Office\Office12\excel.exe" /regserver(quotes
required)->OK