Hello -
I just received this error as well. Changed my eqhost.txt info, and other suggestions as listed in this thread. Here was the solution for me:
- Disable Real Time Protection from Windows Defender
- Shift + Right Click EQ Shortcut - Run as Administrator
I've noticed with the last Windows 10 update, Steam client also will not run games, update games, or install new games unless I completely exit and run Steam.exe as an Admin. Perhaps it's my SECPOL but thought this might help someone else.