Help With SQL Procedure Conversion

Hi Guys, I need some in SQL conversion from Oracle to SQL Server...Here is the procedure in T-SQL..When I run the below SQL in SQL Server, it is going in infinite loop. When I click stop, I am getting the error .......
"Invalid length parameter passed to the substring function."
at the following line
SELECT @RoleID_in = CONVERT(NUMERIC(8, 2), SUBSTRING(@UserRoles_in, 1, CHARINDEX(',', @UserRoles_in) - 1))
-------------
DECLARE @objid_in INT
DECLARE @objclass_in INT
DECLARE @userid_in INT
DECLARE @userRoles_in VARCHAR(3000)
DECLARE @RoleID_in INT
DECLARE @cnt INT

DECLARE csr CURSOR FOR
SELECT * FROM objectACL
OPEN csr
WHILE (0 = 0)
BEGIN --(

fetch NEXT FROM csr INTO @objid_in, @objclass_in, @userid_in, @userRoles_in
IF (@@FETCH_STATUS = -1)
BREAK
SELECT @UserRoles_in = SUBSTRING(@UserRoles_in, 2, LEN(@UserRoles_in))
WHILE (0 = 0)
BEGIN --(
SELECT @RoleID_in = CONVERT(NUMERIC(8, 2), SUBSTRING(@UserRoles_in, 1, CHARINDEX(',', @UserRoles_in) - 1))
SELECT @cnt = COUNT(*) FROM nodetable WHERE objtype = 21 AND id = @RoleId_in
IF ( @cnt = 0 )
BEGIN
INSERT INTO error_report VALUES( 'ObjectACL' , '0' , 'UserRoles refering to Non-existing Role : ' + CAST(@RoleID_in AS VARCHAR) )
END
SELECT @UserRoles_in = SUBSTRING(@UserRoles_in, LEN(@RoleID_in) + 2, LEN(@UserRoles_in))
IF ( @UserRoles_in is null )
BEGIN
BREAK
END
END --)
END --)
close csr
DEALLOCATE csr
GO
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Corresponding procedure in Oracle
---------------
declare
cursor csr is select * from objectACL;

objid_in number;
objclass_in number;
userid_in number;
userRoles_in varchar2(3000);
RoleID_in number;
cnt number;

begin
open csr;
loop
fetch csr into objid_in, objclass_in, userid_in, userRoles_in;
exit when csr%notfound;

UserRoles_in := substr(UserRoles_in, 2);

loop
RoleID_in := to_number(substr(UserRoles_in, 1, instr(UserRoles_in, ',')-1));
select count(1) into cnt from nodetable where objtype=21 and id=RoleId_in;
if (cnt =0) then
insert into error_report values ('ObjectACL', '0', 'UserRoles refering to Non-existing Role : '||RoleId_in);
end if;

UserRoles_in := substr(userRoles_in, length(RoleId_in)+2);

if (userRoles_in is null) then
exit;
end if;
end loop;
end loop;
close csr;
end;
/
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