Automatic plugin installation problems


i have as of today a membership with WMPU DEV, and i have installed the dashboard.
But i have a problem installing plugins.

When i go to the dashboard and click the install button, i get an error message which gives:
Download failed. The destination folder for streaming file does not exist or is not writable.

Unfortunately i have no idea how to make it writable, or make the proper adjustments how to make the folder writable.

When i add new plugins, using the upload function in WordPress, it works perfectly, and the upload gives no error, only when i want to import the plugin or theme i get this error.

Hopefully you can help me with this problem.
I can give login to WordPress admin, FTP and server control panel, no problem offcourse.

I hope to hear from you about this.

Kind Regards,
Tommy Hermans
Magic Radio