You will see Visual C++ Runtime error R6034 when you export a DMX file from an official Blender build. This error is harmless, and will only be seen once per Blender session.

The easiest fix is deleting the VC++ 2008 Runtime libraries distributed with Blender. Browse to your Blender install directory and delete these three files:

• msvcm90.dll
  
• msvcp90.dll
  
• msvcr90.dll

If Blender stops working after you delete these files, install the VC++ 2008 Redistributable package (32-bit[www.microsoft.com]/64-bit[www.microsoft.com]).