SSIS : Conversion text stream DT_TEXT to DT_WSTR

Refering to SUBSTRING (SSIS Expression) documentation:

Returns the part of a character expression that starts at the specified position and has the specified length.

You have to convert DT_TEXT column to DT_STR/DT_WSTR before using Substring() function, you can do this using a Script Component, you can use a similar function:

string BlobColumnToString(BlobColumn blobColumn)
{
    if (blobColumn.IsNull)
        return string.Empty;

    var blobLength = Convert.ToInt32(blobColumn.Length);
    var blobData = blobColumn.GetBlobData(0, blobLength);
    var stringData = Encoding.Unicode.GetString(blobData);

    return stringData;
}

Or if the DT_TEXT length doesn't exceed the DT_STR length limit try using the following SSIS expression:

SUBSTRING( (DT_STR,1252,4000)[RawData], 1, 5 )