@michele 

i disable both(notifications,izap videos)and run again cron/minute but the same

*i dont have any other izap plugin except izap videos

i try to install last night email plus but i get error because i run elgg 1.11 and the plugin wan unable to start because needs elgg1.12

yes i disable izap and run cron/minute but the same.

Add an empty file called "disabled" into the mod/ directory and test again. This disables all plugins temporarily, so you can verify that the problem is not caused by a plugin.

If the cron is executed successfully then delete the "disabled" file and then disable the plugins one by one and check which plugin is creating the problem.

still nothing...no plugin is responsible for that,im pretty sure that the problem is the tons of notifications that piled up and now when i try to run cron/minute server is anable to execute so many tasks.I wonder how i can "clean"the tons of notifications....i dont know maybe i find what is going on next year with the new years enlightening

no i search and i read about that but to be honest im afraid to do that maybe my server crash do you think this is safe?

I haven't seen anything in this thread that shows what's in the error log.  A 500 internal server error should have a fatal error logged somewhere that would tell you what is going on.

hello to all!HAPPY NEW YEARS FRIENDS!!!!!All good to you and to your families!

@beck24 the only referal to cron that i found in 640mb(!!!)of errors is that

[Wed Dec 30 16:18:22 2015] [error] [client 178.59.9.121] File does not exist: /home/openplac/public_html/favicon.ico, referer: http://mysite.com/elgg/cron/minute

also i found those two urls that trigger cron/minute to my site

[Wed Dec 30 18:23:41 2015] [error] [client 66.102.6.251] FastCGI: comm with server "/usr/lib/cgi-bin/php5-fcgi" aborted: idle timeout (30 sec), referer: http://www.google.gr/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CEwQFjAG&url=http%3A%2F%2Fmysite.com%2Felgg%2Fcron%2Fminute&ei=XmeEVpPyJJGgrQO2WA&usg=AFQjCNE1aNN-7f0GNoqqtZ6d3kG322ltsA

[Wed Dec 30 18:23:42 2015] [error] [client 66.102.6.251] FastCGI: incomplete headers (0 bytes) received from server "/usr/lib/cgi-bin/php5-fcgi", referer: http://www.google.gr/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CEwQFjAG&url=http%3A%2F%2Fmysite.com%2Felgg%2Fcron%2Fminute&ei=XmeEVpPyJJGgrQO2WA&usg=AFQjCNE1aNN-7f0GNoqqtZ6d3kG322ltsA

i dont understand thereason even with error logs,so  if anyone understand plese help

any one to help solve that "quiz"?

Just a wild guess. Check your FastCGI url.. most probably its not "/usr/lib/cgi-bin/php5-fcgi"

btw i dnt remember using fcgi in any of the core settings. Are you using fcgi for any 3rd party plugin.?