The Restrict List to Predetermined Values is a checkbox 
that indicates whether a value for the parameter must be in 
the list of values.  For example, if you check Restrict 
List to Predetermined Values and the Initial Value does not 
match a value in the list of values, an error will be 
generated when you accept the Parameter property sheet.  
Similarly, if you set a value for the parameter on the 
command line or in a command script and it does not match a 
value in the list of values, an error will be generated 
when the report is run.  If you check Restrict List to 
Predetermined Values, a list of values will appear in the 
runtime parameter form.  If you do not check it, a combo 
box will appear (i.e., you can enter values as well as 
select from the list).