I just thought I would share this insight which I stumbled upon at KVR:
In the JUCE Demo Host, if a plugin crashes when being scanned, you'll get a red entry in the hosts list of plugins:
"Deactivated after failing to initialize correctly"
As long as this entry is there, the Plugin Host will not try to scan a (hopefully) fixed version of the same plugin, at startup.
The solution is simple, and I thought I'd enter it here, if there are other newbies like myself, who got stuck on this:
Just select the red marked entry in the list, and press the "Delete"-button on your keyboard!
On Mac, it's "Backspace".