I recall this problem. Looking through my archive I found the following (I also have copies of the files concerned) which is clearly the same issue, though the versions are not the same - at least it may point to a solution for the OP:

Steinberg Wavelab 5.01b FIX for Windows VISTA

• Warning! Will only work with version 5.01b

Just copy the comdlgxp.dll and the CommonVcPh.dll to
your Wavelab folder. Overwrite existing files.

Enjoy!


More info for those interested…

Like many others, I was frustrated when I found out that
Wavelab 5 did not run on Vista. Even more frustrated when
Steinberg said that they would not fix the problem for version 5.
Instead, one had to buy the new version 6. Yeah right!

Well good news! I happen to be good at reverse engineering and
I have a solution for you all. I was very curious on finding why
in hell Wavelab crashed when trying to “Open” or to “Save As…”
a file. Well, it looks like the problem comes from some changes in
the comdlg32.dll in Vista. Some wavelab variable gets overwritten
by the GetOpenFilename function inside comdlg32.dll. That causes
the application to crash. By debugging the disassembled code, I was
able to realize that Steinberg could have easily fixed the bug. They only
had to make a minor change in the source code. They wont fix it because
they want to make more money off you!

By The Black Numenorean