There has just been a recent update for CSS Menu Writer v2 that has been released, it is 2.0.3. Is this the version you are using and getting the error with? If you are not using this latest release please login to WebAssist.com and visit the download area to obtain the latest release. When you install it make sure to completely uninstall the previous version before installing the newest version to ensure that no conflicts occur.
If you continue to have this issue please let us know so we can investigate it further.