I had the same problem when C4 arrived and I could'nt purchase C3 for my
The key is to use Transitional Mode (adminstrator settings, compatibility),
here's wat the HELP says:
Enabling compatibility with older versions of Contribute
Contribute 4 offers administrators two compatibility options--one that allows
users with earlier versions to work on the website, and one that does not:
In this mode, users of earlier versions of Contribute can continue working on
the website, along with Contribute 4 users. This lets you evaluate the new
version and set up new roles and permissions without disrupting users with
earlier versions of Contribute.
In this mode, all users must use Contribute 4. Users with earlier versions
cannot work on the website.
Contribute 4 starts in Transition mode by default when you migrate from
Contribute 3. Use this mode temporarily; when you?re ready, transition all
users to Contribute 4 and enable Compatibility Mode.
To enable Compatibility Mode:
In Contribute 4, select Edit > Administer Websites, and then select a website.
The Administer Website dialog box appears.
Select Compatibility from the category list on the left.
The Compatibility options appear in the Administer Website dialog box.
Select Compatibility, and then click Close.
After you enable Compatibility Mode, all users connected to the website must
use Contribute 4.
It's really better to upgrade yourself to the newest version, so you know what
extra options your clients have and you can support them. I managed to get both
C3 en C4(I purchased the upgrade) running on my PC, so maybe that's also an