In the SQLNET.log file, I saw the following error message:

Fatal NI connect error 12560, connecting to:

(DESCRIPTION=(ADDRESS=(PROTOL=BEQ)(PROGRAM=oracle)(ARGV0=oracleORCL)(ARGS='(DSCRIPTION=(LOCAL=YES)(A DDRESS=(PROTO =beq)))'))(CONNECT_DATA=(SID=ORCL)(CID=(PROGRAM=C:\xxx.exe)(HOST=zzzz)(USER=SYSTEM))))

Fatal NI connect error 12539, connecting to:

(DESCRIPTION=(LOAD_BALANCE=ON)(FAILOVER=ON)(ADDRESS=(PROTOL=TCP)(HOST=yyyy)(PORT=1521))(CONNECT_DATA =(SERVER=DEDICATED)(SERVICE_NAME=oraprod)(FAILOVER_MODE=(TYPE=select)(METHOD=basic))(CID=(PROGRAM=C: \xxx.exe)(HOST=zzzz)(USER=SYSTEM))))

VERSION INFORMATION:
TNS for 32-bit Windows: Version 9.2.0.5.0 - Production
Windows NT TCP/IP NT Proto Adapter for 32-bit Windows: Version 9.2.0.5.0 - Production
Time: 04-MAY-2005 13:59:11
Tns error struct:
nr err code: 0
ns main err code: 12560
TNS-12560: TNSroto adapter error
ns secondary err code: 0
Tns error struct:
nt main err code: 530
nr err code: 0
ns main err code: 12539
TNS-00530: Proto adapter error
nt secondary err code: 126
nt OS err code: 0
TNS-12539: TNS:buffer over- or under-flow
ns secondary err code: 0
nt main err code: 0
nt secondary err code: 0
nt OS err code: 0