On 1.8, Market version 3.2.0, you cannot purchase applications.
As a workaround, you can revert to 3.1.5, if you had a Titanium backup.
if not: get Market version 3.1.5 from here: Free File Hosting Made Simple - MediaFireninstall version 3.2.0 with Titanium backup.
Reboot the phone.
Go to the folder you downloaded the file (sdcard/download probably) and install the .apk file with a file manager like Astro or ES file explorer.
Go to Titanium backup and restore version 3.1.5, it will appear in the list.
Reboot the phone and you should be done. I already tried to purchase an app and it worked fine. before it was FC.