In SharpDevelop 220.127.116.1148, I changed our Subversion integration to use SharpSVN instead of SvnDotNet.
SharpSVN exposes more Subversion APIs to managed code, which could result in some nice features in the (far) future - for example, "SVN Diff" right inside the text editor.
But the main reason for the upgrade was that SharpSVN supports Subversion 1.6. If you are using TortoiseSVN 1.6, you need to update to SharpDevelop 3.1. The old SvnDotNet does not work with new working copies.
However, the same is true in the other direction: if you use SharpDevelop 3.1, you must update to TortoiseSVN 1.6. No matter which .NET wrapper or client version is accessing a repository, the underlying Subversion library has the unpleasant feature to automatically upgrade working copies. As soon as the Subversion 1.6 library inside SharpDevelop touches your working copy, Subversion 1.5 clients will no longer be able to access it.
You need to update all Subversion clients on your machine at the same time. SharpDevelop contains a Subversion client:
This entry in the Subversion FAQ describes the problem and offers a working copy downgrade script, in case you decide to go back to a previous SVN client version.