ORA-12154: TNS: could not resolve the connect identifier specified

I have been given a DB account and set of connection information to add into my tnsnames.ora file on my PC. Each time I try and connect I get the following error ORA-12154: TNS: could not resolve the connect identifier specified, yet a colleague who has a different query tool (SQL Developer) can manually input the connection details and connect fine. Can anyone give any clues as to what may be going wrong? The entry in tnsnames.ora is in this format:

OK (0 msec)

Any tips what could be going wrong? it isnt credentials they work fine, it cant be firewall/IP fitering due to my collegue having similar access to me. so it must be something wrong in tnsnames.ora?
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Chakravarthi AyyalaDatabase AdministratorCommented:
what is that OK (0 msec)?
Is that part of thetns entry?
slightwv (䄆 Netminder) Commented:
>>what is that OK (0 msec)?

That is the result from the tnsping.

For the  ORA-12154, do you have more than one Oracle product installed?  You may not be looking at the tnsnames.ora file you think you are.

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pma111Author Commented:
I got it to work with a EZConnect connection method, unsure why the tnsnames.ora method didnt work as it was supplying exactly the same information, a port number. but //hostnames:port/instance name

It was the right tnsnames.ora as our query tool was updating the drop down list of database servers after we edited it.
slightwv (䄆 Netminder) Commented:
>>our query tool was updating the drop down list

Then I would look at the query tool...

Test the config using sqlplus.  If that works, the problem is with the tool.
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