Transact SQL :: Calc Work Date Using Business Days Field In Calendar Table

I created a dbo.Calendar table that stores dates and a work day flag (1=work day, 0=non-work day) so I can use it to calculate the next business date from a date using a function. I'm using a while group to count only the work days and a couple other internal variables but I'm not sure if I can even use them in a function.

Assuming Sats & Suns are all non-work days in April 2014, if my @WorkDays = 10 for 10 work days and my @DateFromValue - 4/1/2014, I would expect my return date to be 4/15/2014.

------ Messages after I click execute on my query window that has my function ------------------------------------------------------
Msg 444, Level 16, State 2, Procedure FGetWorkDate, Line 19
Select statements included within a function cannot return data to a client.
Msg 207, Level 16, State 1, Procedure FGetWorkDate, Line 20
Invalid column name 'WorkDay'.
Msg 207, Level 16, State 1, Procedure FGetWorkDate, Line 22
Invalid column name 'Date'.

------ my function code ----------------------------
CREATE FUNCTION [dbo].[FGetWorkDate](
    @WorkDays VARCHAR(5),
    @DateFromValue AS DateTime )
    RETURNS DATETIME

[Code] ....