Numeric Check MSSQL 2005

Hi,

I am working on MSSQL 2005

I want in table TMPMATERIALORDERED field Quantity should be numeric and greater than 0, if not than the

STATUS should be set to FAILURE and REMARKS should be set to Quantity is not numeric or Quantity is less than 0

In table TMPMATERIALORDERED my filed Quantity is nvarchar(100)

My query gives error says

Msg 4145, Level 15, State 1, Line 3
An expression of non-boolean type specified in a context where a condition is expected, near 'Then'.

Please find my query below and help me in correcting it


Update TMPMATERIALORDERED
Set STATUS = Case
  When Not IsNumeric(Quantity) Then 'FAILURE'
  When IsNumeric(Quantity) And Quantity <=0 Then 'FAILURE'
  Else NULL
End,
Set REMARKS = Case
  When Not IsNumeric(Quantity) Then 'Quantity is not numeric'
  When IsNumeric(Quantity) And Quantity <=0 Then 'Quantity is less than 0'
  Else NULL
End
 

WHERE
      QUANTITY IS NULL
      AND STATUS IS NULL
      
      
Please Help