If you have LabWindows/CVI 5.5.1 or higher, you can specify a negative value for the Output Queue Size when calling OpenComConfig(). This makes write operations synchronous -- when ComWrt() or ComWrtByte() return, they have completed their output operations. I would recommend this as well as switching from ComWrtByte() to ComWrt(). To upgrade online to CVI 5.5.1, go to http://www.ni.com/upgrade and select upgrade to Measurement Studio 1.0.1.
