Your tag database for that project is corrupt. Search for "unable to save tag database" at AB's Knowledge base and there is instructions on how to fix it at the first link. Also, be aware that the HMI Project folder that your project is stored in should not be compacted to save disk space. (I've run into this on occasion).
1. Shut down RSViewME Studio
2. Open a Windows Explorer window and browse to the following directory C:\Documents and Settings\All Users\Documents\RSView Enterprise\ME\HMI Projects and locate the folder that contains your application name and open it.
3. Select the folder Tag and open it. Delete the .cac file in the Tag folder and then return back to project name folder.
4. Select the Cache folder and delete the RDMdata folder.
5. Close and reboot the PC.
