You have deployed your PowerPivot workbook to Sharepoint and are experiencing Data refresh issues.
Before you go chasing your tail, look no further than the following 3 links that discuss what Powerpivot Data Refresh is all about…
1. PowerPivot Data Refresh Whitepaper
2. PowerPivot Data Refresh Account Checklist
3. Troubleshooting PowerPivot Data Refresh
Yes this is a lot of info to wade through, however at the end you will hopefully be wiser and solved your data refresh issue.