Checked Indexes on all tables - nothing out of the ordinary
Ran compact and repair
No change

Try these steps.

1. Compile Database [Debug Menu in Visual Basic Editor].
2. Check for "MISSING" References [Tools - References].
3. Create blank ACCDB file and import all objects.

Also, see Troubleshooter

That got it! Thanks Kevin

1 - (Appreciate the baby steps - i'd have been looking forever!) Did come up with an error, had a red line (...Statements...). Not sure what it was but removed it and nothing broke :) This DID NOT fix the issue however.
2 - References were fine
3 - This fixed it.

I notice a few differences now that it's a new file which is fine. Biggest concern is the global relationships have reset so will take some time getting everything back up and running but at least i'm no longer stuck!

Thanks again

Dan the issues you saw were very likely due to the Global Relationships you had set up in your single file.

To test that theory out make a copy your single file DB backup into a new folder.  (You did backup prior to doing all this right?)

Now open that copy up and remove the Global Relations (GR).  Afterward compact and repair.
Now I bet the split will occur with out a hitch.

BTW - Don't spend a lot of time on resetting your GR.  They are not really used when you have your db split.
This is one of the reasons Richard doesn't spend a whole lot of time and effort on the GR.  Eventually it is you - through your code and processes that control how the integrety is maintained.

The AdHock Relationships should work just fine. i.e. in the query window.

Hi Scott,

(Yep, local backups and cloud backups of everything - even *short term* backups within the database - once you get in the habit, its easy)

Thought i'd humour/humor you and i took the old file and deleted all relationships (And C&R) and you were dead right. This is really handy to know - appreciate you sharing

I'm guessing this will all be covered later, i'm only up to Expert 4 so i'll carry on with it for now but keeping in mind that there will be a better method.

Thanks again

Yeah , that is something you would think that Microsoft would take into account - especially when you run their splitting tool.  Access is a GREAT tool but I do wish that they would bring it into this decade and work some of the issues.

Glad you got it sorted and that you are progressing nicely.  Thanks for letting me know.

Yeah, I don't even like using the splitting tool. I just copy the database file, delete the tables from the front end, delete everything else from the back end, and link them manually.

Great tip!