I’m using WaveLab 9 Pro and Cubase 8.5.30 Pro on Windows 10. I noticed that if I export a mixdown and select Post-Processing on WaveLab 9, everything works like it should. But if export said mixdown normally, close Cubase then open WaveLab and drag the exported wave file into WaveLab, the tab is red and I can’t edit the Cubase project.
I read the manual, and I have the “Insert iXML Chunk” option checked. I’m new to WaveLab and can’t think of other reasons why that isn’t working.
I just discovered I was unable to open a mixdown from Cubase 8.5.30 in Wavelab 9.5.25 if ‘Include iXML Chunk’ was activated in the ‘Export Audio Mixdown’ options in Cubase.
I’ve seen a couple inquiries on the forums about problems like this, but very few discussions, much less answers.
I wrote Steinberg technical support; if they give me a useful answer, I will endeavor to post it here.
Btw. The Link between Cubase and Wavelab is broken if moving the cubase project folder to another location or opening it on another machine (e.g. Mac to Win and vice versa)
Moving a Cubase project folder is always a bad idea since even Cubase itself will not automatically create new files to the moved directory. So I wouldn’t call it broken yet: this needs testing, by ‘moving’ the Cubase directory through making a project backup to the new location.
Sry, this is a little bit off topic 
but moving a project is essential(!) when working home and mobile, this works perfect on different machines, different OS, with recorded audio on any system where the moved projects opened. I asure you
Why not a “Project workspace folder”? Cubase / Wavelab can access all important files relative and not absolute (that’s the real problem!). Moving this “Project workspace folder” to another folder, another machine, Wavelab, Cubase can pick up all relevant files again.
I would be against Cubase and WL sharing the same project folders, simply because what I do in WL isn’t always related to a Cubase project. And the user should have all freedom to organize directories as they like.
As for Cubase directories (I’ve been using Cubase since the Atari versions): You may be using copies of project directories on different computers, but try moving a Cubase to a different location via the OS and your Cubase audio locations will be a mess. I assure you