what version of SQL Developer are you running?
how big is your CSV file?
Also...is your version of SQL Dev using Java bundled with it or does it point to your Java installation? If the latter, which version of Java?
version Information :
Java(TM) Platform 1.6.0_11 Oracle IDE 3.0.04.34 Versioning Support 3.0.04.34
I hate to be THAT guy - but those are all really old. And we redid a LOT of the import logic in version 4.1
I would try it there.
But I am able upload the same csv file into the dev database without any issues in the same sql developer version