Export SQL Server varbinary field to string using Visual Basic script in SSIS?
On line 9, instead of GetType(Byte) you need GetType(Byte()).

Encoding.GetString only takes a byte array; never a single byte, so regardless of the type provided by the framework, what's there is logically not going to work.

If there is another field in the table that comes back as a Byte, you'll need to add another branch to the If statement to handle the encoding (or convert the single byte to a byte array of length 1 and use common encoding code).