CPF5060 error running QsnReadMDT API in SETATNPGM program

I have code that uses the Qsn display data stream APIs ( QsnReadMDT,
QsnPutBuf, ... ). When I have a display on the screen that was built
using those APIs, then press the attention key to run another program
that puts up a display using the same Qsn APIs - I get a CPF5060 -
session cannot send now error.

IBM has sample code that uses these APIs. I compiled and ran low level
services example 3 [1] and get the same error.

The sequence of APIs in my code is:
 QsnCrtCmdBuf
 QsnCrtInpBuf
 QsnCrtScr
 QsnWrtDta
 QsnSetFld
 QsnSetCsrAdr
 QsnPutBuf
 QsnReadMDT

I get the CPF5060 on the call to QsnPutBuf. When I add SETATNPGM to
the mix, my code is waiting on the QsnReadMDT API to return when the
attention program runs. That program runs the same Qsn APIs and fails
on QsnPutBuf.

Am I supposed to suspend somehow the 5250 session of the first
program? This attention program works when the display being overlayed
is a standard CRTDSPF display. It only fails when the base display was
painted using the QSN APIs.

thanks,

-Steve

[1] 
http://publib.boulder.ibm.com/infocenter/iseries/v5r3/topic/apis/dsm1g.htm?resultof=%22%6c%6f%77%22%20%22%6c%65%76%65%6c%22%20%22%73%65%72%76%69%63%65%73%22%20%22%73%65%72%76%69%63%22%20%22%65%78%61%6d%70%6c%65%22%20%22%65%78%61%6d%70%6c%22%20