Well, I've found that error report. Apparently what is causing the issue is a label that counts how many responses have been "yes" on a K2checkbox. the obtained error is the following:
"System.Exception: XPath : "/Root/ClientExpectations/Helpful/YesCount" could not be resolved on this document.
at SourceCode.K2Utilities.XmlFieldHelper.XMLValueInternal(XmlDocument poXMLDoc, String psXPath, Object pValue, String psMethod)
at SourceCode.K2Utilities.XMLFieldMod.GetXMLValue(String xml, String XPath)
at K2Code809.getExpectations(String strQuestion, String strSummary, String strField, ServerEventContext K2)
at K2Code809.Main(ServerEventContext K2)"
The fact is that the control binding is apparently correct...