You definitely want to back up what you have just in case things go south. Some of what you write is a bit confusing to me (like a db is "linked" to a server). If this is a corp network, then I envision the following (NOTE ignores the use of a mdw file):
The master db is split into FE and BE. The BE is stored on a server (not linked to it). Each user gets a copy of the FE to put on their desktop or personal network drive space. Before making any copies, the FE is linked to the BE via the linked table manager, and this is done in the FE, not BE. Each copy will then point to the BE tables. Also before distributing, the FE Trusted zone settings should include the BE location to be on the safe side. Can't recall if each FE needs this for the individual's FE location as well. If so, one way of having to get around dealing with TZ settings on each user's fe after each new FE release is to keep them all in a shared network folder and have them use desktop shortcuts to their copy. The BE shared setting must not be set to open exclusively (this isn't the default value). The FE then gets distributed. Also, each user must have full rights on the folders involved (except maybe the ability to create or delete folders) because Access needs to alter the files, plus create/modify the laccdb file as well as the last user deleting it when Access closes.
The mdw is no longer supported and for the most part, has become archaic. You might want to consider revamping the db's so that they aren't needed. User access control is often governed by a table of users that also contains system level types such as admin, user, supervisor, etc. and is used to control not only who can see/use what, but who gets in. The fact that the number of concurrent users allowed seems to have changed on its own suggests that there is an issue with the mdw file. This could be as simply as your db's not now knowing where to find it.
If I make a copy of the DB and go through the process of splitting the copy DB it will NOT affect the original DB that the users are accessing now, correct?
MAYBE YES. Let's say you copy a pair of db's (fe/be) to your desktop and want to play with it. You delete all the data, figuring that your copied tables are the ones you're deleting from. Imagine then getting a call saying that all the production data is gone (because you're the db admin). Guess why? Your fe copy is still pointing to the network be file because you didn't link your desktop fe to your desktop be.
Before the move and change we never had this file there.
Well, that file is supposed to be there. It's been so long since I had anything to do with the mdw setup that I can't remember much about it, and have to wonder if it was suppressed by the use of the mdw db to control access. If that is the case, it would seem to support my idea that your db's no longer have access to your mdw files.
Last edited by Micron; 02-12-2018 at 12:00 PM.
Reason: clarification
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.