Assign a Velocity Field
Delete it (in the scene)
Stoke crashes - does not display , but also it does not remove the field completely and its impossible to add a new one.
You need to delete Stoke object and recreate it.
Hope it helps.
What type of field is it?
It does not crash here, but I suspect I might have fixed that a while ago (my build is weeks ahead of yours).
If you can provide exact steps with exact object classes used, I might be able to reproduce it if it is still an issue…
It happened to me always and with various (I guess all) sources.
Ok, it does not crash here, but it is actually stuck and does not allow more objects to be added.
Fixing…
Fix is simple.
Open the StokeUI.ms file in the Stoke MX\Scripts folder, locate the line
fn updateVelocityList =and modify the code below to insert the following new lines:
if isValidNode theObj do ( --NEW LINE!
local thePropNames = case classof theObj.baseobject of
(
SimEmber: #(#Spacing, #VelocitySpacing, #ViewSpacing, #TimeResolution, #Discretize, #VelocitySolver, #BoundsType, #BoundsMin, #BoundsMax, #StartTime)
FumeFX: #(#GridSpacing, #Width, #Length, #Height, #velocityScale, #StartFrame, #EndFrame, #PlayFrom, #Playto, #Offset)
Thinking: #()
default: if isValidNode theObj then getPropNames theObj.baseobject else #()
)
for p in thePropNames do
(
theTooltipText += p as string + ": " + (getProperty theObj.baseobject p) as string + "\n"
)
)--NEW CLOSING BRACKET
It was failing inside an error trap attempting to find out the properties of a deleted object… Silly me 
Worked as a charm.