Can't display wireless clients

NPM web interface, WIRELESS tab, show CLIENTS, I get this:

'', hexadecimal value 0x11, is an invalid character.

at System.Xml.XmlEncodedRawTextWriter.InvalidXmlChar(Int32 ch, Char* pDst, Boolean entitize)
   at System.Xml.XmlEncodedRawTextWriter.WriteElementTextBlock(Char* pSrc, Char* pSrcEnd)
   at System.Xml.XmlEncodedRawTextWriter.WriteString(String text)
   at System.Xml.XmlWellFormedWriter.WriteString(String text)
   at System.Xml.XmlWriter.WriteElementString(String localName, String ns, String value)
   at System.Xml.XmlWriter.WriteElementString(String localName, String value)
   at WirelessSummary.CreateClientsXML(Int32 page, Int32 pages, Int32 records, ListOfBO`1 clientList)
   at WirelessSummary.GetClients(Int32 id, Int32 page, Int32 rows, String sidx, String sord)

I can show ACCES sPOINTS fine but not clients. I can expand access point and look at the clients but if I select CLIENTS in WIRELSSS SUMMARy VIEW pull down menu it crashes (See above).