Browser not initiating a POST in Client Initiated Forms based SSSO

I have a similar problem, where the javascript get inserted, but i get the following:

TypeError: __f5action.indexOf is not a function var __f5qsep = (__f5action.indexOf('?') == -1) ? '?' : '&';

F5_Inflate_onevent(document.body,[0x6f,0x6e,0x6b,0x65,0x79,0x64,0x6f,0x77,0x6e],0,function(e){return false;}); document.body.style.visibility='hidden'; document.body.style.display='none'; function __f5submit() { var __f5form = document.forms[2]; F5_Invoke_setAttribute(__f5form,'autocomplete', 'off'); F5_Inflate_value(__f5form.username,[0x76,0x61,0x6c,0x75,0x65],0,'PeteXY'); F5_Inflate_value(__f5form.password,[0x76,0x61,0x6c,0x75,0x65],0,'f5-sso-token'); ; var __f5action = F5_Deflate_action(__f5form); var __f5qsep = (__f5action.indexOf('?') == -1) ? '?' : '&'; F5_Inflate_action(__f5form,0,__f5action + __f5qsep + 'f5-sso-form=user_login'); ; F5_Invoke_submit(__f5form); } if (window.addEventListener) { F5_Invoke_addEventListener(window,'load',__f5submit,false); } else if (window.attachEvent) { F5_Invoke_attachEvent(window,'onload',__f5submit); } else { F5_Inflate_onload(window,0,__f5submit); }

Besides username and password, there is a and a tag

Do i need the specify the hinddden parameter, altough it already has a predefined value ?