If you’re using V-ray, please make sure you've enabled the Batch render setting (V-Ray Render Options > Global Switches under Misc.). In order for V-Ray to allow batch rendering you need to have that checked.
When the Batch Render option is unchecked, V-Ray will render just one frame and then pop up a message saying "please wait for current render to finish".
Make sure you do not have any “non English” characters in the link to the folder or in the file name. If you have characters like for example å, ä, ö,ø, ð, ü or ß, please remove them and see if it works better without them.
This problem should be fixed in the latest version of V-Ray 2.0 for Rhino, so please make sure you have the latest version installed.