If you are running a 32-bit operating system on your web server, MySQL limits you to 31 table joins. liveSite uses table joins to display Custom Form data in Custom Form Views. Therefore, if you are limited to creating 31 fields on a single Custom Form. If you add any more fields, you will get this error message.
If you need more than 31 fields per custom form, you can:
1) Split your Custom Form into multiple forms and link them together, or
2) Upgrade your web server to a 64-bit operating system.