Some elements were deleted because of bad parameters (n)
This project is in use by [Somebody]
Unable to read temporary section file [ID]
Cannot find some Library Parts or Macros.
Other dialogs here.
"Some elements were deleted because of bad parameters (n)" Where n is a number. The number is usually 1, and is never very big. I saw a 7 once. The conventional wisdom is that the elements in question aren't actually project elements, but are corrupted temporary entities of some sort. Bottom line: Don't Worry.
"This project is in use by [Somebody]" Buttons: Open with exclusive access, Open as read-only, Don't Open. It's possible that someone else has it open. Make sure they don't. Usually, the somebody is you, and this warning is the result of a crash occurring before the first auto-save. If this is the case, "Open with exclusive access".
"Unable to read temporary section file [ID]" This sometimes occurs when a Archicad crashes with a section open. It represents a complete non-issue. The section itself is fine, it's the temp file for the section that has the problem. When you rebuild the section, the temp file gets fixed. Do a find & select for the section by its ID and rebuild it. You will get the warning every time you save until you rebuild the section in question. You will also see a dialog warning you about saving the file with the unreadable data. For this dialog, you should always "Save Anyway". This should remind you to find the section and rebuild it.
"Cannot find some Library Parts or Macros." While saving an archive. The proper response is "Save Anyway". Then you'll get a report window saying what's missing. Currently there's a problem with some library part that wants a macro named "Arial". Yes, that's a font. I know. If this the only thing missing, don't worry about it. If there are others, try to find them on the Carrot, load them, and then re-save the archive.