Have something working.
I commented out all the lines of code with calls to SetBackdropColor and SetBackdropBorderColor in HealBot.lua, HealBot_Action.lua, HealBot_Options.lua, and the addon loaded without errors. I copied my config files and got my bar profile to show up (yay!), but not my spell assignments (not sure why those didn't work; easy to add this by hand). The background of the dialog boxes are clear because of the edits but otherwise it's useable for now.
To comment out the stuff: (put a -- in front of the code for each line you want commented out) Careful, there are calls to SetBackdropColor and SetBackdropBorderColor which take up multiple lines in HealBot_Options.lua. Make sure to comment them all out. The code statement is terminated by a semicolon.
I haven't tested in a group yet; only tested on the druid so far.
Copied over the latest retail version just out of curiousity and got setBackdropColor (a nil value) errors...
Found this on the forums:
"... effective in 9.0, no frames have backdrops unless the addon imports/inherits the backdrop template.
this means addons that aren’t importing them now throw nil errors with method “Setbackdrop”. This issue affects a large number of addons."
you prob know all about this.
Lemme know if you want help trying things out.