ewww optimizer error

i have used ewww optimizer plugin to optimize images it did a great work on it but as soon as it is done some fatal error occured and some background scripting is going on which gets me internal server error ..when i contacted my host administrators they said some png images are causing this problem ..i analyzed it in gmetrix and i got this as errors under leverage cached browsing https://gtmetrix.com/reports/www.cellsolutions.ca/4hFpvHAX my website is entirely down now please help

and to add to that issues they said these process are constantly running even after killing them screen shot is posted please help me solve this https://prntscr.com/ddwr8i