Thanks for the tips guys.
I've isolated the problem down to the Event Calendar. Here's what I've done so far...
I've installed the latest version of Event Calendar
I've installed Dataobject Manager (I didn't have this installed before but the new Event Calendar seems to require it)
I've installed Legacydatetimefields (not sure if it's needed though...)
/dev/build/ now runs fine and I have 2.4.0. However, the Event Calendar is well broke :-(
I run into an immediate problem with this error on both my site and the CMS:
"Fatal error: Call to a member function AbsoluteLink() on a non-object in C:\wamp\[path]\SilverStripe\event_calendar\code\CalendarUI.class.php on line 17"
The offending code looks like this:
var controller_url_segment = '" . $controller->AbsoluteLink() . "';
var current_url_segment = '" . Controller::curr()->Link() . "';
The code in my old version of Event Calendar used to look like this:
var controller_url_segment = '" . $controller->URLSegment . "';
var current_url_segment = '" . Controller::curr()->URLSegment . "';
Changing the code to the old version creates more errors. Removing those lines altogether allows the site and the CMS to load up, but the module fails to load properly in the CMS (of course).
So, what now? Should I be playing around with the Event Calendar code, or is there some other dependency I'm unaware of that I have to install? Or something else??