On Umbraco v4.5.2.

When clicking on any node in the backend, we're getting the following error:

At /umbraco/editContent.aspx?id=1047 (Referred by: http://www.example.com/umbraco/): System.NullReferenceException: Object reference not set to an instance of an object.
   at umbraco.controls.ContentControl.addControlNew(Property p, TabPage tp, String Caption) in d:\Dropbox\Dev\UmbracoSource_v4\umbraco\presentation\umbraco\controls\ContentControl.cs:line 272
   at umbraco.controls.ContentControl.CreateChildControls() in d:\Dropbox\Dev\UmbracoSource_v4\umbraco\presentation\umbraco\controls\ContentControl.cs:line 121
   at System.Web.UI.Control.EnsureChildControls()
   at umbraco.controls.ContentControl.OnInit(EventArgs e) in d:\Dropbox\Dev\UmbracoSource_v4\umbraco\presentation\umbraco\controls\ContentControl.cs:line 153
   at System.Web.UI.Control.InitRecursive(Control namingContainer)
   at System.Web.UI.Control.AddedControl(Control control, Int32 index)
   at umbraco.cms.presentation.editContent.OnInit(EventArgs e) in d:\Dropbox\Dev\UmbracoSource_v4\umbraco\presentation\umbraco\editContent.aspx.cs:line 101
   at System.Web.UI.Control.InitRecursive(Control namingContainer)
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

The frontend of the site is working fine, so I suspect something wrong in the preview cache? Right clicking the node => publish fixes the issue for any given node, but there are thousands of nodes so doing that for each one will take a very long time.

I've tried right click content => "republish entire site", and /umbraco/dialogs/republish.aspx?previews=true. Neither of them have fixed the issue.