tn5250 problem on Win32: SBA order to row 1 column 0 fails

I am new to this list. I downloaded and installed tn5250-0.17.3-setup.exe
and executed it to install the tn5250 client on my Windows 2000 Professional
machine. Testing it with a server, I got an error that does not occur with
other tn5250 clients I have tried. I think the error is caused by an SBA
order to row 1 column 0 in the outgoing data stream used by the server.
The IBM manual seems to say that this should work. (By the way, my
server is not a real AS/400 machine, but is local software I have developed
to test tn5250 and tn3270 clients.) Details and a trace are given below.
Does anyone have any ideas on this? Thanks.

Details....

The tn5250.exe client was installed by downloading and executing
tn5250-0.17.3-setup.exe via http://tn5250.sourceforge.net.

The "5250 negative response" 4-byte error code is hex 10050122,
which, according to the IBM manual (section 13.4 of "5494 Remote
Control Unit Functions Reference" SC30-3533-04), means an invalid
row/column address was sent to the tn5250 client in an outbound
data stream. The invalid row/column seems to be row=1 column=0
in the SBA (Set Buffer Address) order. But several other tn5250
clients allow this, provided the SBA is followed by a SF (Start
Field) order, which it is in this case. See section 15.6.4 of
the IBM manual. For example, this works ok with the Mochasoft
tn5250 client, and other IBM and Hummingbird clients.

In the trace below, the dump of the outgoing telnet data (from
server to client) is shown after the tnsend() line. The telnet
response from the client is shown after the tnrecv() line.
Each starts with the usual 10-byte SNA header.

tnsend(): xi=1 len=92 opt=0, sent 92 bytes:
0000: 005A12A0 00000400 00030440 04110008 *.!......... ....* *.Z.........@....*
0010: 1101001D 2006DF11 01015CC5 95840201 *..........*End..* *.... .....\.....*
0020: 50005CC7 96021550 00021606 60E30216 *&.*Go..&....-T..* *P.\....P....`...*
0030: 4860E302 164F4011 16501D40 00240050 *.-T..| ..&. ...&* *................*
0040: 02175000 22021846 00D98581 84899587 *..&......Reading* *..P."..F........*
0050: 40402013 17010452 0000FFEF *  ..........* *@@ ....R....*
* >> pcselect: calling oper rtn 5 for xsoctbl[] entry xi=1
Telnet server: xi=1 opern=5 state1=3 flag1=005F senddsp=0 readdsp=0
tnrecv(): xi=1 maxlen=6000, read 16 bytes:
0000: 000E12A0 00000480 00001005 0122FFEF *................* *............."..*
cnvin5250() called: xi=1 datalen=16 maxlen=6000 tmpbufsize=6000
** Error 4 in incoming 5250 data stream or header. xi=1 dlen=14 flag=80
...Error bit on in SNA header: Bad data stream to 5250. code=10050122

- Dave Edwards