Problem With Case Expression

In the Portal1 case expression in the script at the bottom I would like
to replace where the result 1 is returned, with the substring function
returned as Portal

{SUBSTRING(Field1, CHARINDEX('tonep', Field1) + 4, (CHARINDEX('.txt',
Field1) - 8) - (CHARINDEX('tonep', Field1) + 4))}

However, I am experiencing errors. I think it is because The substring
function will not return a number as the case expression expects so I
must incorporate cast or convert, but do not know how. Can you help???




SELECT portal1 = CASE WHEN len(Field1) > 5 THEN 1 ELSE '' END,
SUBSTRING(Field1, CHARINDEX('tonep', Field1) + 4, (CHARINDEX('.txt',
Field1) - 8)
- (CHARINDEX('tonep', Field1) + 4)) AS portal,
Table.*
FROM Table