See the following help document:

Troubleshoot Adobe Download Assistant

http://helpx.adobe.com/creative-suite/kb/troubleshoot-download-assista nt.html

If you are unable to resolve the matter following that document, you could try downloading the trial version from the page linked below.

Be sure to follow the steps outlined in the Note: Very Important Instructions section on the download pages at this site or else the download will not work properly.

CS6: http://prodesigntools.com/adobe-cs6-direct-download-links.html