I write for a few different groups, some with Robohelp 6 and
some with 7.
For life to be good, I really need to have versions 6 and 7
installed on my machine. I have a license for each - my department
bought version 6, and another department bought me a copy of
version 7. But - when I installed 7, 6 was un-installed.
I can't develop my other projects in 7, because they won't be
able to support it once I'm done (because they still have 6).
I currently have the following all installed and peacefully
coexisting side by side on the same PC.
So I'm going to go so far as to blatantly claim that version
6 and 7 together will work. What you can't do is to expect to use 7
to edit projects and still use 6 to edit the same projects.
There is another issue that might be at play too. If 7 was
purchased as an upgrade for 6, the licensing probably prevents you
from leaving 6 installed and also installing 7. You would have to
have purchased full versions of each to do so.