WFE:s responds different when working with Powerpivot

Hi all.

Have a problem where the environment is as follows.

SharePoint 2010

2 WFE  server

1 App server

SQL 2008 R2

When clicking on a PowerPivot link i get two different respons 

1. Sucess entering the Powerpivot file

2. Read or edit file

Is there anything that i have missed?

Thanks