Time machine errors

[Howard Brazee]

A month ago I was having the Time Machine fail window pop up. In the
past I would ignore it and it would go away for 6 months, but this
kept on. I solved it with the following procedure:

1. Enter the time Machine

2. Scroll back it time for a few generations

3. Select the folder(s) to delete

4. Under the "Action" item (or gear icon), select the delete option
you want.

But not the window is popping up again.
My oldest backup is from January, 2013.
My Time Machine drive ha 978.51 GB of 1 TB.
MyMac has 408.85 GB of 499.25 GB.

That would seem to be plenty big enough - I haven't really done much
to change my backup requirements in the last year.

Any ideas of what to look for?