Why my ubuntu/apache getting “server reached MaxRequestWorkers setting”?

I have ubuntu 14 and apache mysql on a cloud server with 512 mb ram. I am getting "server reached MaxRequestWorkers setting". every few hours. I have the server MaxRequestWorkers at 150. I have been trying to figure out what is going on for past few days. What am I overlooking? Below are the partial logs. I noticed that server goes non responsive/wont load website once the (inteal dummy coection) is logged. Please help.

Thank you

::1 - - [21/Apr/2016:00:54:39 +0000] "OPTIONS * HTTP/1.0" 200 125 "-" "Apache/2.4.7 (Ubuntu) PHP/5.5.9-1ubuntu4.14 (inteal dummy coection)" ::1 - - [21/Apr/2016:00:54:56 +0000] "OPTIONS * HTTP/1.0" 200 125 "-" "Apache/2.4.7 (Ubuntu) PHP/5.5.9-1ubuntu4.14 (inteal dummy coection)" ::1 - - [21/Apr/2016:00:55:04 +0000] "OPTIONS * HTTP/1.0" 200 125 "-" "Apache/2.4.7 (Ubuntu) PHP/5.5.9-1ubuntu4.14 (inteal dummy coection)" [Thu Apr 21 00:55:09.862087 2016] [mpm_prefork:error] [pid 16248] AH00161: server reached MaxRequestWorkers setting, consider raising the MaxRequestWorkers setting Blockquote