Fatal Error -26499: Internal Error - ptVUserVars

Hi

I've have recorded a Web-HTTP/HTML script in URL mode in Loadrunner a couple of times and I get same error message every time:

Fatal Error -26499: Internal Error - ptVUserVars->_hDfePE is unexpectedly NOT NULL after xfeLrwSrvNetTaskItemPrimaryCreate.

It happens within my login transaction.

lr_start_transaction("Login");

    web_submit_data("testxx.xxxxxxx.com_2",
        "Action=http://testxx.xxxxxxx.com/?class=form-signin",
        "Method=POST",
        "EncodeAtSign=YES",
        "RecContentType=text/html",
        "Referer=http://testxx.xxxxxxxx.com/",
        "Snapshot=t14.inf",
        "Mode=HTTP",
        ITEMDATA,
        "Name=__RequestVerificationToken", "Value={__RequestVerificationToken}", ENDITEM,
        "Name=ReturnUrl", "Value=", ENDITEM,
        "Name=Username", "Value=xxxx.xxxxxxxxxxx@xxxxxxxx.com", ENDITEM,
        "Name=Password", "Value=x", ENDITEM,
        LAST);

I´m new to loadrunner can anybody help and explain why this happens and suggest a work around?

BR Birre