Error: System Error

More fun and games with Storage in my development app on my F5.
---
Error: System Error
Details: 'Failed invoking <symbol>'
Time: 2019-01-13T05:28:29Z
Part-Number: 006-B2697-00
Firmware-Version: '12.00'
Language-Code: eng
ConnectIQ-Version: 3.0.7
Filename: QS_RACE
Appname: QsPlus
Stack:
- pc: 0x10005b6e
File: /Users/.../Documents/watchApp/raceQs_Racing/source/main.mc
Line: 56


I'm sure we humble devs aren't meant to see "System Error"s.
On immediately re-running my app it ran without a murmer.
The referenced line 56 was :
Storage.setValue("GUID", GUID);

Sure starts to smell like there is a latency issue with Storage