I'm sorry to comment on this old report, but I'm having the same issue.
When trying to disbale the function keys temporaryly through ctrl+a !, following error is shown
$ :source /usr/share/byobu/keybindings/f-keys.screen.disable :source: command not found
The affected ubuntu version is current 14.04 with byobu 5.74 (Screen 4.01.00).
I'm sorry to comment on this old report, but I'm having the same issue.
When trying to disbale the function keys temporaryly through ctrl+a !, following error is shown
$ :source /usr/share/ byobu/keybindin gs/f-keys. screen. disable
:source: command not found
The affected ubuntu version is current 14.04 with byobu 5.74 (Screen 4.01.00).