Domain Controller Error

I currently have a set of workstations receiving a Could Not Contact Domain Controller error and need an idea of how to resolve the issue. The workstations do not receive this error when in our office but when at our warehouse they do receive it. I think it may be related to a timeout issue but not sure how to correct it. The circuits and all settings are correct as they can check email and enter information but they receive this error still and I need to correct it so we can mirror some directories. Any idea’s?