The form has been closed

This is the most common error that occurs while designing the Info-Path form. It also says the form template that is published in the Form library location is invalid. I had this issue a lot of times and most of the times the common thing i was missing while designing the New form is, i am not checking the option "Enable browser-compatible features only" while opening a "Blank" form. Once i am able to check that option while designing the form, then it was working fine for me. below is the screen capture for reference.

Timeout expired. The timeout period elapsed prior to completion of operation or the server is not responding

Last weekend our SQL servers are rebooted. This had the instance of NW2007 configuration DB. on mondya morning  the Pending Tasks and the New Tasks are not able to be viewed by the concerned approvers. When approvers clicking on the Tasks they are getting unexpected error. In the event viewer it says "Cannot find a corresponding human workflow task id for this task".

Event Type: Error

Event Source: Windows SharePoint Services 3

Event Category: None
Event ID: 0
Date: 11/22/2010
Time: 9:41:40 AM
User: N/A

Computer: COMPUTERNAME

Description:
Nintex Workflow; Build: 11100 (http://DOMAINNAME/_layouts/NintexWorkflow/ApproveReject.aspx?List=27d20a40-c30f-4a8c-978d-f9a1d772f02f&ID=937&Source=http://DOMAINNAME/AllItems.aspx)

Cannot find a corresponding human workflow task id for this task.

For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp.
 
Then we disabled custom error mode to get the detailed error message. Below is the error page information.
 

It seems like the connection between the Web front ends and the Databases of the Nintex workflow DB is missing.

Nintex suggested to check the connection settings between Web Front End and the server runnning the Nintex Workflow DB. We did the following things to get the issue reolved.
 
a) Go to SharePoint Central Administratioin --> Application Management
b) Under the Nintex Workflow Management click on "Database setup".
c) EDIT the Configuration Database that is already setup.
d) Following are the settings that has already setup
   Database Server, Database Name, ("Connect to an exisiting Database" checked)Database Authentication
   is "Windows Authentication".
e) Clicked on "Ok" at the end of the page.
 
That's it. The magic is it reset the connection between the Web Front End and the Server connecting the Nintex Worklfow database.
Everything is working fine now.
Thanks to the Nintex support for asking to check the connectivity.