Firstly, ensure that you are using the most up to date version of the Arnold plugin.
When encountering problems with renders, the first thing you should do is generate a log file. Open the Log file (under Diagnostics) and search for the word "ERROR". Most of the time you will find the source of the problem in that ERROR message.
A Guide to Reading a Log File
As this is a frequently asked question we have provided both the question and answer in this thread.
Lee Griggs
Arnold rendering specialist
AUTODESK
