Unable to re-enable plugin

Friends,
I got adaptive images working with your help last july .. (see https://wordpress.org/support/topic/plugin-not-working-for-me-21/) . You helped me understand that jetpack was getting in the way of it functioning. As I recall, I disabled jetpack and things started working.. but content delivery was much slower.. so I turned it off after a while.

I’m now back to thinking I’d rather have adaptive images that render well on mobile devices. I’ve updated the plugin, disabled jetpack. but am still not seeing images sized correctly on mobile devices or in Chrome using the responsive emulator.

a couple of clues I do have.. I note that the adaptiveimages chache exists.. but is now empty (I cleared it since last july) .. also.. when I tried putting (actually uncommenting ) the lines

location / {
rewrite \.(?:jpe?g|gif|png)$ /wp-content/plugins/adaptive-images/adaptive-images-script.php;
}

in my wp-config.php files I get the following server error

Internal Server Error

The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator, and inform them of the time the error occurred, and anything you might have done that may have caused the error.

More information about this error may be available in the server error log.

the safari console has the following info when that happens

[Error] Failed to load resource: the server responded with a status of 500 (Internal Server Error) (base, line 0)
[Error] Failed to load resource: the server responded with a status of 500 (Internal Server Error) (base, line 0)

Any help much appreciated !!!
thanks so much

-jc

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