Delay in opening of office document

Hi all,

I am facing a very problem and I am not able to trace the exact reason behind this problem.
I am working on a winform application having late bind excel object.

1) Application is running and excel object is not created yet.
******* if user opens any office document with double-click it opens up in 2-3 seconds.

2) Application is running and excel object has been created.
******* if user opens the office document with doubleclick it takes 1 minute.*
******* if user opens the same document with File>Open it opens in 2-3 seconds..


Please give some suggestion.
Thanks in advance.