Hi there,
ive been trying to set up 404 custom page,but still getting empty page.

i followed these rules: troubleshooting

my .htaccess works,ive tested it ,look for the attachment

any idea,how to fix this issue?

Hi,
So your SEF URLs work correctly, but when you enter non-existent URL, you get a blank white page instead of 404?

yes, my SEF work corectly,only 404 pages are not working.

The blank page usually means that some PHP error has been encountered. Please enable error reporting on your server or check the server's error logs to find out some information about the error and post the message reported here.

okay,nevermind,i get some error page,but its not exactly what i wanted.that's joomla 404 page,
just check it, www.forgym.eu/
so what would be your advice now?

Try disabling the "Parse Joomla SEO links" option in JoomSEF's Configuration on the Advanced tab (you need to enable the Professional mode first to see it). But please note that components that use their own router or the default Joomla router for SEF URLs will stop working (you can check this on Manage Extensions page in JoomSEF). If you use only the core Joomla components, there shouldn't be a problem.