Since the upsizing - look at your FE table View.
Do they resemble Globes (indicating SQL Server) with arrows (indicating linked tables)?
In the FE table objects, double click (open) a linked table.
Does the table's data appear?
Scroll down to the last record (the one with a *). Can Data be entered?
After entering a record, highlight the entire last recently entered record (click on the most left border, highlight the entire last record), press Delete. Can record be deleted?
If all of this works, my suggestion is to download your e-data to a new LOCAL table (lets call it MyEDataImport).
Forget ADO at this point.
Then create:
Import the edata into the local table MyEDataImport. Perform any data cleanup.
An Append query using the MyEDataImport Table as the source and update the Linked Table where the data should reside.
A Delete Query to delete the last e-data in the MyEDataImport Table.
The linked tables can take care of the heavy lifting.
By breaking the task into multiple sequential steps, it increases the odds of success and makes troubleshooting easier for each step.