Themeroller doesn't explicitly support 1.2. Use 1.2.1.
There's actually only one Themeroller. It supports 1.0.1, 1.1.2, 1.2.1, 1.3.2, 1.4.0. Just leave the version parameter off the end and select the version from the drop down.
The themes should work find if you are using an earlier minor release. (e.g. 1.2.0)
Minor updates tend to be pretty compatible, though, so consider updating your project to 1.2.1.