If Windows refuses to let you replace your plug-in with a new version with a message about being in use, it means that DigiView is still using it or it is a Zombie (abandoned.) This really should not happen but if something goes very wrong with the plug-in and it stops responding to the DigiView application, DigiView tries to kill the process. If Windows can not kill it for some reason, it stays in memory and and the disk copy is locked.
If this happens, first make sure that every signal using your plug-in is disabled. If that is not the problem, then open the Windows task manager (usually available through cntrl-alt-delete or by right-clicking on the task bar) and review the Processes list. Find your plug-in's name in the list, click on it and select 'End Process'. If it is listed multiple times, end all of them. Now you should be able to copy over the new version of the plug-in.