Genome wide association studies

I'm having trouble following your question and I suspect others might as well.

What code is being run to produce this error? An internet search of this error message doesn't provide much else, so perhaps additional context would be helpful.

Here's a google group forum related to gapit that mentions the error,!topic/gapit-forum/HaDIFmT-zFU

I encourage you to review the following guide, FAQ: Tips for writing R-related questions.
For example, the guide emphasizes asking coding questions with a reprex . You may have noticed that many people here request issues come in the form of a minimal reprex , that's because asking questions this way saves answerers a lot of time helping you get your issue resolved, reducing the number of back-and-forths requires.