Hi,
Make sure that ‘Allow users to browser-enable form templates ' check box is checked in the InfoPath form services. To check this follow the below steps.
1. Open SharePoint Administration (Start -> All Programs -> Microsoft office server -> SharePoint Central administration).
2. Go to Application management tab.
3. Click on ‘Configure InfoPath forms services' in InfoPath forms services section.
4. There you will find the check box in ‘User Browser-enabled Form Templates‘section.