Hello Chris,
Thank you for using the Cisco Small Business Support Community. I'm sorry to hear you're having trouble with the captive portal, and I hope I can help.
The easiest way to bypass the captive portal and get back into the AP is to connect your PC via Ethernet to the same router or switch that the AP is connected to. Once you are connected, you can use a tool like FindIT to open the web configuration utility and make necessary adjustments.
Please reply back with any additional questions you might have with this problem, and I'll do my best to help you.
If you want to download the FindIT tool, here's a link to the download page: https://software.cisco.com/download/navigator.html?mdfid=282828524&i=rm
In addition, I found an article on our Knowledge Base regarding captive portal configuration on the WAP321 that may be helpful: http://sbkb.cisco.com/CiscoSB/GetArticle.aspx?docid=70662d287cab491a831c5274307389f4_Captive_Portal_Instance_Configuration_on_WAP121_and_WAP321_A.xml&pid=2
If this post solves your issue, please remember to mark this question as resolved!
Best,
Taylor