Issue definition:Whenever you submit an infopath form "The form cannot be submitted to the Web server either because your computer is offline or because the host server is currently unavailable. If this problem persists, contact your network administrator"

Reason:
Ther are several reasons for this.
1. ISA server not configured properly
(or)
2. DNS not Configured Proerly
(or)
3. https ssl mappings not done properly using Alternate Access mappings

The above are the high level reasons for this issue. But, In our case, we deleted the root site (http://servername/) by mistake and this issue started bugging. InfoPath needs this root site to host the Infopath applications. When the form is actually published, SharePoint marks this location as the host.

Fix:


Create a root site. Below are the steps:
1. Access the SharePoint Central administratoin
2. Click on the 'Application Management' tab
3. Click on 'Define manged Paths'
4. in the Path field, enter "/"
5. select 'explicit inclusion' from the drop down and 'OK'