SVN commit Error "Commit can only commit to a single repository at a time."

I'm using an eclipse with "Subclipse" installed to commit my changes to a repository that located at my DropBox folder. I've created a repository using Tortoise.My actual project sits in the root of repository folder but not in a trunk or branch or tag folders. I successfully created,checked out and committed several times , but lately I've begun to receive an error on commit : org.apache.subversion.javahl.ClientException: svn: E200007: Commit failed (details follow): svn: E200007: Commit can only commit to a single repository at a time. Are all targets part of the same working copy? org.apache.subversion.javahl.ClientException: svn: E200007: Commit failed (details follow): svn: E200007: Commit can only commit to a single repository at a time. Are all targets part of the same working copy? And nothing can be committed... What causing this problem and how can it be resolved ???