I have definitely the same problem.
Sometimes user can register but sometime it cant.
I tested myself.
For the failed registration, "Could not register new user.", the user name was recorded and the date of registration was always 1970/1/1.
I deleted the "failed regisration". I tried to register again with the same settings e.g. settings of XOOPS and user name, email address....etc. It worked sucessfully.

The thing that I did is change the settings of user profile e.g. min length of user id...etc. And then CHANGE Them BACK to original one. That's mean I theorectically didnt change anything!
But it work not for long. "Could not register new user." will appear after one day. I have to do the same things aagain to avoid that!!!!

I tried many many method and search so many. I still cannot found any "real" solution to it.

I dont know why it happen just try and error for so many times. Now I found the above is the only way that I can "solve" the problem.

My settings

xoops 2.2.4 (traditional chinese ver)
Linux host
PHP version 4.4.4
MySQL version 4.1.21-standard-log

I am serious to this problem. Many thank to peopl who really can help.

I can post attached photos in the CBB forum and it can showed up previously. But I dont know what is going wrong. Now the attached photos of newtopics doesnt show up anymore. But the photos of old topics was not affected. The options of show up photos was selected in the CBB modules.
Can anyone tell me how to fix the problems?
Thanks.