OK I figured it out. First I thought it was because I used a For Each...Next loop to iterate a set. Then I realized that I was not trying to write to the enumerated value in any case.
Finally it dawned on me that there needs to be an Assignment
padTexture = padTexture.padRight(textureLength + 2)
My fault but somehow I got the mindset that the compiler would throw out something that should be part of an assignment - apparently not even with Option Strict on.