Welcome Jan!
I guess X6 or X4 is something like a version number? Usually the version specification would indicate some particular feature which might not import correctly, rather than blocking the import completely. But if there's an option for X6, I certainly would use it.
The only reason I know of that causes the runtime error, is the file being too large. There are other reasons, it's just that's the only one I know. If the file isn't huge, then there's some other problem happening, and we'll probably need to ask developers.
It looks like you have installed the 32-bit version of Inkscape. Is that because you're using a 32-bit system? Or some other reason? I just want to rule out potential problems related to installing Inkscape.
I have found some info in Inkscape's FAQ about needing to install UniConverter to open certain Corel Draw files. It does not look like it would apply to yours, but something here might ring a bell?
https://inkscape.org/en/learn/faq/#how-install-uniconvertor-windowsIf your files aren't from one of those special versions of Corel Draw, then it would probably be best to contact developers. IRC would probably your best bet.
https://inkscape.org/en/community/discussion/