Russell can you please elaborate on the issue? What actually happens? I don't have a very large tnsnames.ora file, but one that has about 150+ entries. some with SID and most with SERVICE_NAME and some even fashioned, but I have not had any problem with properly formatted entries with 3.2 as well as EA4. Hence i am curious as to the issue you are experiencing.
This is just a shot in the dark, but have you checked your tnsnames file to see if anything besides the entry name (and commented lines) begins in column one? Although sqlplus will usually parse such entries successfully, some of the other tools have had issues with them in the past... they seem to misparse the entry, which often messes up the processing of subsequent items.
Here's a quick example, with spaces replaced by periods for readability:
# good entry
# bad entry
If memory serves, only the entry name is actually supposed to begin in column 1... pretty sure I found that documented somewhere, back when I first encountered the issue. So if this is indeed your problem, I suspect that the official verdict would be that your tnsnames file is bad and needs to be corrected.
Again, this is just a wild guess.
If tnsnames.ora file throws off SQLDeveloper send in the details.
You can also use OCI + tns connection type -> connect identifier- which will not have SQLDeveloper code parse the tnsnames file - leaving it to the oracle client code.
1/tnsnames.* files are checked
2/tns connection type->network alias options has a pull down list of tns addresses found.
3/There are various ways of specifying your tnsnames directory, including ORACLE_HOME, TNS_ADMIN and from the preferences tnsnames directory.in tools->preferences->database->advanced