Let’s try with older version at first, here is 7.7.1: https://download3.manycams.com/support/771JDYUD749274CJDZXC/ManyCamSetup.exe?v=7.7.1
BIG NOTE: downgrading is not officially supported and installing older version over newer may result in data loss (mostly effects). It is recommended to backup your data before downgrading: make a copy of entire %AppData%\ManyCam folder (notably settings and state_storage files) before installing old version (close ManyCam completely by Ctrl+Q). On any error/data loss install newer manycam, close manycam and replace that folder from you backup. Making a periodic backup of this folder is a good idea.