i found another thing ,,,
i have WFE server ,, when i submit the form from it ,, the process started normaly
but when i submit the form from the Application server ( same K2 server ) i got the error

any idea !

Could you check the registry key as mentioned on the linked post?

Also is SharePoint web application running in NTLM or Kerberos?

Could be an double hope issue, need to configure Kerberos correctly.

If K2 and SharePoint installed on distributed servers then we need to configure SPNs between K2 Server and SharePoint. Refer K2 documentation to configure Kerberos using SPNs.

the registery key for the loopback ?! yes i checked them and they are disabled.

its running NTLM ,,,

i did not do anything except running the configration analysis in all servers ,,

now any machine can submit the form , ony the one application server ( same K2 server ) gives the 401 error.

double hub issue from my understanding please correct me if i am wrong

when the authintecation path from the requested machine to the k2 server >= 3 in my case i have the folllowing

From the requester machine to SharePoint WFE servers  (Step 1)

From the WFE servers to the K2 application server (Step 2 )

,....

i will have the issue if the infopath form servers will count as step

From the requester machine to SharePoint WFE servers  (Step 1)

From the WFE servers to the application server (infopath service) (Step 2 )

From the application server to K2 Application.

As the topology i have the following

2 SharePoint WFE server NLBed.

2 Application servers one of the servers is the k2 application server.

2 DBs Clusterred.

and i am using Passthrow authentication.

please advice , if i am facing the double hub , i should be able to submit the form from the first place wright ?!

ok now i will start to lose my mind ,,, 

yesterday ,, all machines could submit any form successfully i did the following to for that ,, 

1) i have two WFE servers i activate the K2 features only on server A, it works the only thing was that i cant submit the form from the k2 server other than that it ok.

but when i opened the the k2 files under the 14 hive just to see which file was causing the problem( last time i will try understand k2 :D) 

I notice that the file version is not the same in Server A and B, so the trivial thing is to unify them ,,, so i run the activation feature for k2 from the central admin , after it finished. 

the problem is back and on all servers ,,,  :S