I have a bizarre remote desktop issue

I own 2 businesses. I have had RDP setup on both business pc’s and home pc for several years. All run xp pro. Suddenly, I can access business #2 from home but not business #1. However, I can log into the business #2 from home then log into business #2 from it. That tells me that there isn’t a problem with business #1 accepting connections or home making connections. Anybody know what could be the problem? Thanks in advance.

Update… I went to business #1 and cannot connect to home but can thru business #2, so the communication problem seems to be between home and Business #1 and vice versa. They are the same internet provider but #2 is different.