Hi CK, can you give us a screen shot of the tax screen, so we can take a look at what you have put in?

The usual cause of this is that the employee is just a baby and working babies don't pay any CPP until they are 18.  Check the year of the birthdate.

If this is not the cause, then please post the setup as Marj suggested, including the settings under Setup, Settings, Payroll, Incomes to see if the income field for the salary field you are using has the checkbox for Calculate taxes.  This would affect all employees using that income field.  Also check to make sure there are linked accounts setup for CPP under the same area, though I think Sage 50 will tell you these are missing.