Attached is a copy of popular ActiveX control ActiveBar 2.0 - basically abandonware at this point but used in a lot of popular projects. It contains a custom property window that stores information in the form's .frx file. When opening a project in tB, it imports correctly, but when opening the form you may see an "Invalid Layout File" error, and then when opening the custom property page, none of the properties show up.

ZIP:
AB2.zip

What it should look like:

Error on opening:

What custom property window looks like in tB: