The CON command returns a syntax error or an input error when used like this:
out1 = CON ( grd1.landuse CN 'forest', 1, 0)
GRD ERROR - Syntax Error at or near symbol SP'forest', 1, 0)
out2 = CON ( 'grd1.landuse CN ''forest''', 1, 0)
GRD ERROR - Unable to open the input grid: GRD1.LANDUSE CN 'forest'
The CON command does not support grid.item notation on character items in the logical expression.
Use the SELECT or TEST commands to structure a workaround. Consult their documentation for details on how to use these commands.