PROPSYS.dll is not a file that Legacy installs. A Google search of the Internet reveals that PROPSYS.dll problems occur when key operating system files become misconfigured, deleted or damaged.
Please visit https://answers.microsoft.com/en-us/windows/forum/windows_vista-performance/propsysdll-error-message/6684b65e-b23e-4040-a92f-de2fbec93808 for the solution.
If the error continues then you can try a system registry repair. There are several utilities available to do this. Some cost money and some are free. We have had success with Ccleaner from Piriform. You can download the free version at https://www.ccleaner.com/ccleaner/download.
Optionally visit https://download.cnet.com/free-window-registry-repair/3000-2086_4-10606555.html. This is a reputable site that also offers a free Windows registry repair tool. The download is free and there is a video preview that you can watch.