[GNC] Can't find the file sometimes

[Heide Wang]

I just updated from my Gnucash 2.6 to 4.9. Where can I find the update instruction for 4.9? I know the basic is same as the old 2.6.  I kept two set of account on Gnucash, sometime I can go to the file to switch account, but sometime when I switch, it said " the file xxxxxx.Guncash file could not be found, the file is in the history list, do you want to remove it?” I never remove the file. I want to find out what did I do wrong?
I am using MOS Catelina 10.15.7

Thanks for the advise as always.

Heide