I even try to move the mod folder away and replace it with a mod folder that is from the other web app, still not working.

and that other web app on the same server also get the Form is missing __token or __ts fields problem...

What can i do?

Have you named the file you created in the mod folder "disabled"? The name must fit, i.e. is must be "disabled" and not "disable".

Also, can you narrow down the possible reason for the error? When did it start? Was it after updating Elgg or after adding a new plugin? If it started after adding a new plugin, you could remove the folder of this plugin from mod and run http://<your.site.url>/upgrade.php to get rid of this plugin. If it started after upgrading Elgg: which version? If it's Elgg 1.8.14, then upgrade to Elgg 1.8.15 as this might fix the issue.

the name is correct

and the reason that trigger this error varies, some times u log out and can't long in again, sometimes seems no reason...

However i used a strange way to tackle the problem at the end

just download and install the elgg step by step, after that go back to open ur original web app

it works again =.= (don't know wt happened, maybe it change the .htaccess? or the htaccess_dist?)

In fact, i'm using virtual machine, both apache in mac and windows could get the problem fixed... 

Can anyone tell me why? or can i have a more simple way to tackle this next time?