invalid length parameter passed to the left or substring function in sql server

create procedure getdata
@subcomponent varchar(50)
as
begin

declare @var varchar(50) =@subcompname
;WITH CTE AS (
    SELECT Sno, Comp, SubComp,
    LEFT(FromValue, PATINDEX('%[0-9]%', FromValue)-1) As FromLetter,
    CAST(RIGHT(FromValue, LEN(FromValue) - (PATINDEX('%[0-9]%', FromValue)-1)) as int) As FromNumber,
    LEFT(ToValue, PATINDEX('%[0-9]', ToValue)-1) As ToLetter,
    CAST(RIGHT(ToValue, LEN(ToValue) - (PATINDEX('%[0-9]%', ToValue)-1)) as int) As ToNumber
    FROM
    (
    SELECT Sno, Comp, SubComp,
       LEFT(SubComp,
          CASE WHEN CHARINDEX(' to ', SubComp) >; 0 THEN
            CHARINDEX('to ', SubComp)-1
          WHEN CHARINDEX(',', SubComp) >; 0 THEN
            CHARINDEX(',', SubComp)-1
          END
       ) FromValue,
       RIGHT(SubComp,
          CASE WHEN CHARINDEX(' to ', SubComp) > 0 THEN
            LEN(SubComp) - (CHARINDEX(' to ', SubComp) + 3)
          WHEN CHARINDEX(',', SubComp) > 0 THEN
            CHARINDEX(',', SubComp)-1
          END
       ) ToValue
    FROM T
    ) InnerQuery
 )

 SELECT Sno, Comp, SubComp
 FROM CTE
 WHERE LEFT(@Var, PATINDEX('%[0-9]%', @Var)-1) BETWEEN FromLetter AND ToLetter
 AND CAST(RIGHT(@Var, LEN(@Var) - (PATINDEX('%[0-9]%', @Var)-1)) as int) BETWEEN FromNumber And ToNumber

Quote:

"invalid length parameter passed to the left or substring function in sql server"