My colleague can't use Zoho docs as "You don't have permission to access Zoho Docs."

My colleague can't use Zoho docs as "You don't have permission to access Zoho Docs."

Hi, 

My colleague, who has been using Zoho doc all the time, suddenly cannot access zoho docs as it show "

You don't have permission to access Zoho Docs.

Can someone tell me what happen?