Problems with uploading files to a sub wp-installation

Hi

I’m running a site for some friends of mine and we use wordpress 3.3.1. Now we want to change the site so I have uploaded and installed a testsite in a subfolder so I can work with the new site and when it’s done, I will move it to the rootfolder.

The problem is that I can’t upload files or pictures to the testsite. It works well on the main site,and it’s the same filepermissions on both uploadsfolders, and yes the testsite has a uploadsfolder under wp-content.

It seems that I have to change the url or something to get wp to know where the files should go.
I get this errormessage from wp when I try to upload pictures

Couldn’t move the uploaded file to /customers/mysite.se/mysite.se/httpd.www/testsajt/wp-content/uploads/2012/04.

The url to the testsite is http:/mysite.se/testsite/ (the main site “mysite.se” is called something else in reality but I believe you know what I mean)

I think that the error is in this url: /customers/mysite.se/mysite.se/httpd.www/testsajt/wp-content/uploads/2012/04.

Thanks in advanced.
sussiny