i have built a workflow using k2 using infopath process wizard

when the workflow starts and a workitem is assigned to a specific user , i try to submit the infopath form that is displayed at that point of the process .i am using infopath client to view and edit forms ;

however , ana error occurs when submitting my form :

infopath cannot subit this form

an error occurred while this form is being submited

the SOAP responseindicates an error occured in the server:

server was unable to proccess request ----> the worklist item cannot be completed due to the following reasons: the given key was not present in the dictionary