Red X on all topics in RoboHelp file

I'll assume this is a red x next to each file in the left hand topic panel and not a red x against entries in the table of contents. I'll also assume your colleague is using RH2019, not an earlier version.

First, make sure all the project files and folders have been included in the zip file. Sometimes we see that only the xpj or rhpj file have been zipped up, not all the htm, image, css, js etc files that are needed.

If the zip file looks like it contains all the correct files, are you using RH2019 (New interface) or RH2019 Classic? Try deleting the files off your hard drive, unzipping the file again and open the project with the same version of RH as your colleague - to make sure you're using the correct version, open Robhelp from the start menu, rather than double-clicking on the project file.

If your colleague is not using RH2019 yet, then we'll need to start again.

Let us know how you go checking the above and what your colleague is using if none of that helps. A screenshot of what you see might also help.