Hi Pravin,
I failed to reproduce the behavior you described on Windows XP with TestComplete 8.70 Enterprise and Microsoft Office 2007 installed. So, please clarify a few moments:
1. What operating system do you have?
2. Which version of Microsoft Office (or Excel) is installed on your machine?
3. Make sure that the ACE driver is installed on your machine. If it's not installed, you can download it from Microsoft's web site:
http://www.microsoft.com/downloads/details.aspx?familyid=7554F536-8C28-4598-9B72-EF94E038C891
Please, provide me with the results so I could help you faster. Thanks :)