No idea.

A small number of people have reported such problems. The vast majority have not.

It is therefore server dependent. I have never seen it myself.

I would dearly love to nail this problem to help out the small number of people who have experienced it.

However, without additional information I really can't help.

You could look in your PHP log, but a couple of people who reported this problem could find nothing there.

The only practical solution I can suggest is to move to another server.

Kevin, I am using wamp server on localhost. I will try it on my server.

Btw, where can I find the PHP log. Should I turn Php log from the htaccess or is there another way ?

@Kevin You're right its a server issue. I am using it on my live server and it works.

Thanks.

OK, good news!

I still wish I knew what the server issue was so I could help people fix it!

I tried on localhost but nothing on php error log.

Btw,I have more questions.

I followed the instruction on readme.txt for flexreg.

Activated form, flexprofile, flexreg.

I created new fields for a new user registration. I also put

1. _name
2. _email
3. _username
4. _password
5. _password2
6. adding more fields

Also tried to change it to

1. name
2. email
3. username
4. password
5. password2
6. adding more fields

But when I trying to register I got duplicate fields. One from the original elgg registration fields and the one that I have created.

How to override the default elgg fields, what fieldnames should I use ?

Also creating a new field from the instruction (by using  existing fieldname)  giving me error:field name doesnt exist. Tried using above fieldname (both with _ and without _)

Its mentioned that there are seven special fields:

_name
_email
_username
_password
_password2
_first_name
_last_name

I thought those are the fieldnames I should use in order to override the elgg reg fields. CMIIW

You don't need to add the email, name, username and password fields in your registration form - just the *new* fields.

You can use the special underscored field names in your registration form templates. But you do not need to add them to your registration form as the system always has those.

Aha...

I thought it replaces the standard elgg registration fields.

Thanks Kevin, its a super-awesome plugin. 

Yup Kevin.  Still digging the template tags. Haven't tried it yet.  Very helpfull if there is an example of the template to be altered and used.

Other than that super-awesome.