what is error (-10011)

That is the 'system overload' error.... It means Core Audio could not handle the load being placed in it for whatever reason and so playback stops...

There are many possible reasons for this... ranging from too slow a hard drive... to... too many plugins running at the same time... Just google Logic Pro System Overload or even simply Logic error 10011 and read through a few of the many threads relating to this problem...

It has so many different causes, all you can do is read up and see which applies to you, if any....

As AOS mentions, it's often the case that Logic can't pull data off the drive fast enough, it sometimes happens with external drives. Are you using a Firewire 400 drive on a Firewire 800 port?

Also, does this happen at the beginning of a project or later on as Regions using a lot of Plugins come into play?

Possible solutions:

-Increase Preferences/Audio/ Process Buffer to Large

-Increase Preferences/Audio/System I/O to 256 (or greater)

-If you've frozen some Instrument tracks, unfreeze them

-Sometimes playing the project all the way through once, restarting after Logic stops playback until you've made it all the way through.

-Quit any programs you have running before booting Logic.

-Too many plugins demanding resources at the same time.

If your using high end Reverbs as Inserts it's more economical to use fewer of them as sends.