SessionNotFound, while still getting heartbeats

I am converting my app to connect to a different platform (Integral) from where I already have it working (Fortex), but I am catching a SessionNotFound when I try to send a MarketDataRequest to Integral and not when I use the same code to request data from Fortex. The only difference between the two is in the config files, which are identical other than the obvious login credentials for the two different platforms, and for Integral I have "SocketUseSSL=Y" and I am using FIX 4.3 instead of FIX 4.4. Even after I am told that the session does not exist, I continue to send and receive heartbeats for both sessions, so how am I getting a SessionNotFound and what can I do to correct it? Thanks in advance for your help!

Here is the code:

private void send2(Message aMessage, SessionID aSessionId) {
try

{ setHeader1(aMessage.getHeader(), aSessionId); System.out.println("session existence: "+Session.doesSessionExist(aSessionId)); System.out.println("session lookup: "+Session.lookupSession(aSessionId)); Session.sendToTarget(aMessage, aSessionId); }

catch (SessionNotFound aSessionNotFound)

{ aSessionNotFound.printStackTrace(); }

}

And here is the print out from the two compared, with Fortex first:

session existence: true

session lookup: FIX.4.4:SenderCompID->FTSDEMO_QUOTE.FORTEX.NET[in:2,out:2]

OUTGOING: quickfix.fix43.MarketDataRequest(8=FIX.4.49=15335=V34=249=SenderCompID50=SenderSubID52=20110621-08:57:09.28156=FTSDEMO_QUOTE.FORTEX.NET55=EUR/USD128=146=1262=1263=1264=1265=0267=0269=0460=410=220)

<20110621-08:57:09, FIX.4.4:SenderCompID->FTSDEMO_QUOTE.FORTEX.NET, outgoing> (8=FIX.4.49=15335=V34=249=SenderCompID50=SenderSubID52=20110621-08:57:09.28156=FTSDEMO_QUOTE.FORTEX.NET55=EUR/USD128=146=1262=1263=1264=1265=0267=0269=0460=410=220)

And here's what I get at this same point with Integral:

session existence: false
session lookup: null
quickfix.SessionNotFound
>>> 001
at quickfix.Session.sendToTarget(Session.java:587)
at STXjune17_2011post1$MyApp.send2(STXjune17_2011post1.java:592)
at STXjune17_2011post1$MyApp.getMarketData(STXjune17_2011post1.java:745)
at STXjune17_2011post1.main(STXjune17_2011post1.java:1153)