This worked for me with Eclipse 3.7.2 and CDT 8.0.2:
- Open the project properties | C/C++ Build | Discovery Options.
- Click the button by Clear discovered entries now:.
- Rebuild.
It is seems to be a new feature in CDT 8. I have had this “Invalid project path: Duplicate path entries” problem for years, and this is apparently the newly provided solution.
Before doing this there were duplicate paths under C/C++ General | Paths and Symbols | Includes tab. I could not get rid of these. They only appear when Show built-in values is checked, so they are apparently generated somehow. After doing the above they were replaced with a set that did not have duplicates. The only difference is that the same settings appeared under Assembly, GNU C, and GNU C++. Previously they were different sets. The ones for Assembly were empty, for example.
So far the problem has not returned.