Using Adobe Dreamweaver and another Subversion client on the same computer can prevent your site from interacting with the Subversion server.
Third-party client software can update your local site's Subversion meta data to a newer client version, which is unsupported by Adobe Dreamweaver CS4.
Third-party Subversion clients can include:
You can find additional clients at Apache Subversion.
You're using Adobe Dreamweaver CS4, which supports the Subversion client libs 1.4.5. And you're using TortoiseSVN (1.5.x), which is supporting client version 1.5, on the same computer. Once you touch your local site using TortoiseSVN (for example, submit a file), the local Subversion meta data of your site is converted to version 1.5. Because of this conversion, Dreamweaver can no longer interact with the Subversion server. The newer Subversion client format is not backwards compatible with the 1.4 format supported by Dreamweaver.