hm, might be a install problem?
after processing 3.5.3 download / unzip / start / set new sketchbook path,
how/what you copy your old sketch source?
please show copy or snapshot your exact error msg.
if i use (ONLY, without the server running )
/ File / Examples / Libraries / Network / SharedCanvasClient
and start it i get ERROR
java.net.ConnectException: Connection refused: connect
PLEASE test exactly same example code