Problems reinstalling Lion

Hello,

I recently purchased a new mac pro and need to sell my old mac pro which has lion installed. Like a dummy I deauthorized the computer and wiped the drive but now I cannot reinstall Lion. It is just stuck searching for an authorization in the reinstall Lion section. Please help.

Your old Mac Pro that had Lion installed, did it ship with Lion or did you update to it?

I updated to it

Use the original OS disks to format the HD and then reinstall the original OS. Whoever you sell it to wouldn't be authorized to have Lion on it anyway.