i had the same problem using elgg_view_form() and it was because the action file wasn't correctly defined in my_plugin/start.php.

@sachin and @zenin please check elgg path in database, check you have set correctly or not.

Is it on all actions, or just when you're trying to do something specific?

make sure in database tables, and config file ...

for correct webroot and dataroot

It can be an error of mod_rewrite. Check your htaccess. Also try uploading a new version of Elgg.

@Sachin : good debugging. If you are having wrong site path, then the error is common to all site actions.  As a guest, the number of actions are limited (login, registration, forgot password only). That may be why you missed other actions.

@Sach:
from your testimg - cpudl you see why the missng end-slash does *not (would not) cause problems at other times ? I've felt before that we need a simple edit-check for such inputs -- whether there is a traling slash or not ;-) and stop the Admin right there ! Maybe even a parse_url for stronger validation..

I for once agree with dhrup. We could use a parse_url tool for stronger validation, but this topic seems like it would go under elgg features or elgg plugins. It wouldn't be hard to build a url parser.

(1)    strlen(<input>)    == '/' or !=
    play around with terminal char?!

(2)    filter_var(<input>,FILTER_VALIDATE_URL)
    make sure it's ok

(3)    parse_url(<input>)
-->
    [scheme] => http
    [host] => hostname
    [user] => username
    [pass] => password
    [path] => /path
    [query] => arg=value
    [fragment] => anchor

if further detailed verificn desired

so, who's detailing the code + writing up trac ticket ?
($today->iam ? ($toolazy || $busy) : $lolz}){ //betcha this actually executes correct;)

I started having the same problem just out of the blue. "The action file for login was not found." I am very much a novice on elgg, but I can pretty much understand most things. Can someone help me, in lay terms, as to what to do to correct this? I cannot login, register, or pretty much do anything beyond the login screen. Also, the login screen changed from the simple horizontal box to a wierd vertical one. Is this a mod problem or conflict? I am very confused about that. I greatly appreciate any help. I am using the latest version - 1.8.? only had working for about a week... Thanks!!!