Hi there!

I have the same problem but with
PL/SQL Developer
Version 9.0.6.1665
293.81420 - 6 user license
Windows 7 (64-bit) 6.1 Build 7601 (Service Pack 1)

Oracle Client version 10.1.0.2

PL/SQL - ORA-12154: TNS:could not resolve the connect identifier specified
tnsping.exe prodcu2 - OK
sqlplus.exe apps/<somepass>@prodcu2 - OK
sqlplusw.exe - OK