You don't need to download Protege 4.3.
First of all Protege 4.3 is old, and second this problem does not
have anything to do with differences between Protege 4.x and 5.x
versions. The simple solution to this problem is what Samson said:
make sure you have GraphViz installed, and also that Protege
settings point to the right path to the dot.exe.