ORA-12203, but I can do a tnsping

Hi everybody!
I have a singular problem, I can't connect through Forms Developer to my
Oracle Database, I receive the

"ORA-12203: TNS unable to connect to destination"

I already have the listener running.
The curious thing is that if I stop and restart it again, it seems to work for
a couple of minutes, but after some time this error begins to appear....
I also can tnsping from the machine I'm trying to access the database:

Attempting to contact
(ADDRESS=(COMMUNITY=tcp.world)(PROTOCOL=TCP)(Host=10.0.0.42)(Port=1521)
OK (50 msec)
The listener.log reports the following:
29-NOV-2004 09:19:10
*(CONNECT_DATA=(SID=NUMAR)(CID=(PROGRAM=C:\ORANT\BIN\ifrun60.EXE)(HOST=SJ-ESM)
(USER=esanchez))) *
(ADDRESS=(PROTOCOL=tcp)(HOST=10.0.1.147)(PORT=1584))
* establish * NUMAR * 0

I'm using Oracle 8.1.7 on Redhat 9.
Any help would be appreciated.
thanks in advance,
  -eduardo s.m. Received on Mon Nov 29 2004 - 09:26:31 CST