When Microsoft Word has been upgraded, for example from Word 97 to Word 2000, it sometimes recognizes the Startup path for the old version as well as its own Startup path. If Lao Script for Windows was installed for the old version, and is re-installed for the new version, it is possible for two separate (and possibly different) copies of the Lao Add-In to be loaded when Word starts.
If this occurs, look under Tools - Templates and Add-Ins, and you will probably see that the Lao Add-In (LSWin*.dot, or possibly WWLao.wll) is listed more than once. The folder for each copy is indicated when that Add-In is selected. Remove the copy of the Add-In from the previous Startup location, to ensure that only the current version of the Add-In is being used. (Or, if the version is correct, you can clear the Startup location entry under Tools – Options – File Locations).