doxygen & dot

[Raghu Vadapalli]

I am using the latest version of the doxygen 1.3.9,graphviz packages 
& Fedora Core 1 to generate call graph documentation for my source
tree.   After generating proper call graphs for a while it stops
working and spits out

"Generating call Problems running dot. Check your installation!
Problems running dot. Check your installation!
Problems running dot. Check your installation!"

I don't where/what to look for with log or sign of crash.  

Thanks
Raghu.