Now my 3D design is finally ready to be printed, I noticed something really curious: groups are just not exported, just missing from the design. When testing this, even creating three solids, of which I group the first two, only the third solid is exported in the STL file.

Now this is annoying, but wouldn't be a problem if you could select all and then choose 'ungroup'. I have about 155 groups in my design and when I 'select all' and then choose 'ungroup', it brings a message up for every group (so times 155...) that ungrouping will delete dependent object, i.e. delete the actual group. It doesn't show you where the groups are. I can see the group count, but not the location on the design. Only by selecting a single group, you can ungroup it without losing it.

What to do to export the complete design?

Thanks for the answer. I think I was not clear enough. I need to export everything in one file. It doesn't export the parts of the design that are in a group, therefor I need to identify the groups and Ungroup them. As I can't select all and Ungroup them, as it will delete the contents of the group, how do I identify the groups without having manually to click everywhere to see if there are any groups? My design is quite complicated.

Next time I'll put everything on a individual layer, not in groups.