ERROR: Could not open file : DISK_ERR

That's a strange one. When you get DISK_ERR, can do do anything (eg. list files) or is it totally dead?

Are you sure it's not that something is using the pin for something else, or even potentially a wiring issue? Calling E.connectSDCard would cause the card to be re-initialised, so if something had confused it (for instance dodgy power wiring?) that would fix it.

To detect it, I think you could check for readFile returning undefined, or even catching any exceptions that get thrown. However I'd maybe check wiring first, and put a capacitor across the power lines right near the SD card just in case. It really shouldn't happen in normal use.