Heads Up - if you downloaded Sage 100 2018 PU1 --- Sage apparently slipstreamed a fix and re-issued the update with the same filename on 12/21. If you have it saved somewhere on your computer or in file storage (Dropbox, etc) best to re-download.
There appears to be an issue with the original PU and sites that did NOT have payroll.
It's not entirely clear whether Sage has already updated the 2018.1 or if one KB entry got head of another.
In this entry, they claim to have updated 2018.1 -
https://goo.gl/LvPTvc
In the main 2018.1, they seem to be saying to wait for an update -
https://goo.gl/QaVBBu
My money is on Sage having updated with a new 2018.1 however, as with all things Sage, YMMV.
Naturally, all this confusion would be completely eliminated if any subsequent re-issue of the PU was made with a new filename.