The Windows Vista OS is known to have compatibility issues when running serial communications programs on multicore processors. This issue is because it allows multiple cores to work on the same program, which can cause synchronization issues. To solve this, use the “Set Affinity” to 1 core. There are various ways to do this (Google “Windows Vista Affinity”). When the program is running, one way to change that setting is to right-click the application from within the Task Manager and then set the affinity.