Mr Red -

Many(?) programs recommend that you "uninstall" your old version prior to installing an upgrade - where the upgrade contains "the whole package." If files from the older version remain, they can "confuse" the new one, or enough of the old one is left to permit it to try to load, but it can't work with files modified for the new version.

An upgrade that only adds or "tweaks" a few files, though, may depend on the earlier version being present. A "licensed" upgrade may also look for the old version, and refuse to install if its not there.

A program can "call" for a .dll by its generic name. Windows does have a "search hierarchy" that prescribes the order in which various directories should be searched, and can usually find the right file if its in any of the "usual locations."

Many programs, though, will call for the .dll by its full path name. If the call is to a particular file in a particular location, the call will fail if the file has been moved or deleted. Windows will not search elsewhere in this case.

A common "failed call" source is the shortcuts in the Startup directory. Shortcuts are invariably to a particular file in a particular location - and will usually fail if the "target" file is moved or deleted.

It is considered good programming practice to get subordinate files by generic calls that allow Windows (or whatever the OS) to look for them - where possible; but doing this in every case would prevent you from having more than one version of any program on the machine.

In any case of a "missing" .dll, or any other missing file, the critical thing that needs to be determined is "what process is looking for it?". Randomly copying .dll files elsewhere is not likely to provide a "real" solution to most such problems.

John