Theme Errors vs VB upgrades (question)

[onehost]

I am currently in dispute with a theme coder. at the time the theme was installed.
it was installed on VB 4.0.8 and since then I now have VB 4.1 - The theme has errors.

90-99 validation/html errors
9 warnings
unable to see private messages (coder left out of theme, coder error)
Missing Images thoughout the entire theme (coder error)
Explaination points that popup randomly during
the posting process...(error unknown)

The coder is trying to blame everything on me because he designed this
on 4.0.8 and wants me to downgrade back to 4.0.8 in order to do testing,
which I am not really sure how to do anyway...I have themes that are
less then 4.0.8 and run with no issues, I have mods clear back to 4.x with
no issues, but he is insisting that I am using 4.1 and that is the reason
all these errors exist... I do not believe that statement at all...the minor
difference is so slim that there should be almost no errors if any regardless.

What do you guys think? Do you really think a difference like this
would produce this many errors, or do you think it is just bad coding?