The error means that Test Studio is unable to deserialize the Silverlight app, because of a missing quote, however we haven't seen this error before and it will be very difficult to determine what is causing the issue without a local reproduction. Are you getting this error during the compilation or during the execution? If this is a compile error, we'll need to provide us with a copy of your test project(in a .zip file). If you're getting this error during execution, then the only way to be able to reproduce this is to provide us with a direct access to your Silverlight application.
If you feel any of this information is sensitive, you can submit a support ticket which is confidential, unlike this forum. Thanks for providing the info we need to best assist you.
All the best,
the Telerik team