web.reg_save_param (web_reg_save_param) Error in VBScript Vuser

I have been unable to get web_reg_save_param to work correctly in a VBScript Vuser. The functional reference documentation for it is non-existent, but it registers fine when the script is run, but it always fails with:

Error -26377: No match found for the requested parameter "UserSID". Check whether the requested boundaries exist in the response data. Also, if the data you want to save exceeds 256 bytes, use web_set_max_html_param_len to increase the parameter size [MsgId: MERR-26377]

Here is my code:

iResult=web.reg_save_param("UserSID", _
  "LB=<USERSID>, " & _
  "RB=</USERSID>, " & _
  "RelFrameId=1, " & _
  "Search=Body, " & _
  "LAST")

'-----------------------------------------
' Execute the call
'-----------------------------------------
iResult=web.custom_request(sQuery, _
  sRestUrl & sQuery, _
  "Method=GET", _
  "RecContentType=text/xml, " & _
  "Referer=, " & _
  "Snapshot=t04.inf, " & _
  "Mode=HTML, " & _
  "Body=, " & _
  "LAST")

 Here is what is being returned to be searched with the item of interest bolded:

<SESSIONS serDuration="0.406"><SESSION><LINK HREF="/v1/rest/session">/v1/rest/session</LINK><USERSID>351345874000113011</USERSID><USERNAME>sysadmin</USERNAME><LASTTRANSACTION>2014.08.19.11.12.02.546</LASTTRANSACTION><EMPLOYEESID>348347481000138004</EMPLOYEESID><EMPLOYEENAME>SYSADMIN</EMPLOYEENAME><EMPLOYEEACTIVE>TRUE</EMPLOYEEACTIVE><CONTROLLERNUMBER>1</CONTROLLERNUMBER><CONTROLLERSID>348347481000014255</CONTROLLERSID><WORKSTATION>NCORISON0-WKS</WORKSTATION><WORKSTATIONID>351639173000156178</WORKSTATIONID><SEATED>TRUE</SEATED><SEATEDAPP></SEATEDAPP><SUBSIDIARYSID>348347481000137001</SUBSIDIARYSID><SUBSIDIARYNUMBER>1</SUBSIDIARYNUMBER><STORESID>348347482000111009</STORESID><STORENUMBER>1</STORENUMBER><REGIONSID>0</REGIONSID><DISTRICTSID>0</DISTRICTSID><WORKSTATIONTYPESID>0</WORKSTATIONTYPESID><ACTIVE>TRUE</ACTIVE><DEPARTMENTNAME></DEPARTMENTNAME><HISECSBSSID>0</HISECSBSSID><HISECEMPLSID>0</HISECEMPLSID><HOMEURL></HOMEURL><PERMISSIONS/><PREFERENCES> ... </PREFERENCES></SESSION></SESSIONS>

 Thoughts? Also, is there some other way to access the Response Body? Please note that this problem is common to both LoadRunner 11.52 and 12.0.