On December 20, 2019, attempting to patch EQ left people with an, "Error: The downloaded file is incomplete of was corrupted", error message.
As of 1 p.m. EST on December 21, it still has not been resolved.
To fix it, go
and click Download in the upper left corner. Save it in your EverQuest folder. Then start the Launcher.
No word from Daybreak has been seen on this issue.
UPDATE: Daybreak has fixed this error. There is no longer a need to use the file that was linked above.