This makes no sense to me. Can you copy/paste whatever error it is you're getting?
You should be able to download/run Space as an eval *without* first having purchased it.
1. navigate to https://support.juniper.net/support/downloads/
2. below, where it says "Find a product", type in "Space" and hit the blue "Find a product" button on the right. The page should update with "Download Results for: JUNOS SPACE NETWORK MANAGEMENT PLATFORM", defaulting to the latest version on top.
3. if you're installing it as a virtual appliance on a VMware host select "Image for Virtual Appliance" (the ova file), or if you're installing on a VVM platform, select "KVM Image for Virtual Appliance"
Prior to the actual download, you may need to authenticate yourself again, and then "Agree" to the big red EULA. After that, it should start downloading to your browser.
Hope that gets you going.