Can't access repository with OSX client

I have a SmartSVN professional license, and I have repositories set up on a remote server.

I can access these repositories from my main work PC, running the Windows SmartSVN client.

We are using https for the connection.

I am trying to get the OSX client to connect to the same repositories, and falling at the first hurdle.

I get the following error when attempting to connect to the repository server:

My googling has lead me to believe this can be caused by:

*incorrectly configured repositories (not the case, I can connect from the windows client)
*proxies (I don't have any proxies configured on my mac)
*firewalls (I don't have any firewall configured, other than the one on my router which both the PC and mac go through). Also I can access the repositories through the web interface from my mac.

Any suggestions?