插入火车功能 - 无法找到变量“optimismBoot”

I'm new to R and RStudio and have been experimenting with predictive modeling. The following train function works without parallel processing but when I implement doSNOW makeCluster, I get the error shown below related to a variable named "optimismBoot". I've searched in vain for a resolution, tried installing and uninstalling packages, but nothing works. Any insight appreciated.I'm new to R and RStudio and have been experime