Does anyone know what this error message means?

Sketch uses 29716 bytes (11%) of program storage space. Maximum is 262144 bytes.
Atmel SMART device 0x10010005 found
Device       : ATSAMD21G18A
Chip ID      : 10010005
Version      : v2.0 [Arduino:XYZ] Oct 20 2016 15:20:47
Address      : 8192
Pages        : 3968
Page Size    : 64 bytes
Total Size   : 248KB
Planes       : 1
Lock Regions : 16
Locked       : none
Security     : false
Boot Flash   : true
BOD          : true
BOR          : true
Arduino      : FAST_CHIP_ERASE
Arduino      : FAST_MULTI_PAGE_WRITE
Arduino      : CAN_CHECKSUM_MEMORY_BUFFER
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CPU reset.
processing.app.SerialException: Error opening serial port '/dev/cu.usbmodemFA131'.
	at processing.app.Serial.<init>(Serial.java:125)
	at processing.app.Serial.<init>(Serial.java:66)
	at processing.app.SerialMonitor$3.<init>(SerialMonitor.java:93)
	at processing.app.SerialMonitor.open(SerialMonitor.java:93)
	at processing.app.AbstractMonitor.resume(AbstractMonitor.java:110)
	at processing.app.Editor.resumeOrCloseSerialMonitor(Editor.java:2240)
	at processing.app.Editor.access$2400(Editor.java:77)
	at processing.app.Editor$DefaultExportHandler.run(Editor.java:2218)
	at java.lang.Thread.run(Thread.java:745)
Caused by: jssc.SerialPortException: Port name - /dev/cu.usbmodemFA131; Method name - openPort(); Exception type - Port not found.
	at jssc.SerialPort.openPort(SerialPort.java:167)
	at processing.app.Serial.<init>(Serial.java:114)
	... 8 more
Error opening serial port '/dev/cu.usbmodemFA131'.

Looks like you have the wrong serial port selected in the tools menu.

hmm no I don't think so. This happened after sketch upload and Arduino (mkr zero) would not work after this. Multiple computers would not recognize Arduino. after hitting the reset button multiple times to set it in perpetual boot loader mode I was able to upload new sketches and it seems to work.

mhart9:
mkr zero

That's a pretty critical detail you chose to leave out of the OP. I'll leave this for someone who knows the zero.

thanks...

Also I didn't exactly leave it out, if you look at the error message is states the chip type...

mhart9:
Also I didn't exactly leave it out, if you look at the error message is states the chip type...

I didn't recognize it as zero. When asking questions here it is best to go ahead and give the details of what you have and what you're doing instead of assuming that they can be inferred from something else. If you really want real help that is. Don't be afraid to be verbose. Extra details that we don't need will never hurt. But leaving out details that are needed can be a real impediment. Here you posted nothing, absolutely nothing aside from the compiler output. For others who might not recognize the port name, you probably should have also included the fact that you are running linux. Telling what particular flavor would probably be a good idea. As would any details about the particular setup and how it is connected to the computer and what else is connected to it.