Mark, the Raster Calculator expression being reported in the dialog is:
""w1dem <= "100""
You can't directly compare a grid with a string in arcpy map algebra... based the screenshot of your model I'm guessing the expression you are using is something like
w1dem <= Value
So it looks like your output of Get Field Value is coming out as a string not float. The way to fix that is to modify your expression like this:
w1dem <= Float(Value)
or set the output data type parameter of Get Field Value to Double instead of Any value. You may need to do both. I'm not at work to try it.
Worth a try anyway!