Accessing Netsuite’s sandbox using SuiteTalk

You must use a different URL for the WSDL reference.  Below is the current one form the Netsuite help, but this could change with newer versions.  I found it in thehelp. Additional Resources : Frequently Asked Questions : FAQ: SuiteFlex : Web Services FAQ  of the online help.

Can I use Web Services with my sandbox account? 

Please note that the URL for the WSDL differs between your production account and your sandbox account. If you want to use Web services with your sandbox account you will need to use the following URL for the WSDL:

https://webservices.sandbox.netsuite.com/wsdl/v2010_2_0/netsuite.wsdl