hell!! 

it looks like i found the solution and some workarounds for all of my problems

1. "my redirect bug"
i edited the config.smf.php and changed the mosurl from http://www.myurl.org//index.php?option=com_smf&Itemid=46&
to http://www.myurl.org//index.php/component/option,com_frontpage/Itemid,1/

thats funny because now the link in main menu point to the forum (like it should be) and the login redirect to the joomla index (like it should be)

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2. "my uninstall bug"
i thought its a result of the redirect bug descripted above. so i took the index url http://www.myurl.org//index.php/component/option,com_frontpage/Itemid,1/ and wrote it in the joomla login form module....option "login redirection URL" and logout redirection url"

now after login and logout the login form redirect me to that adress and no error appear.

the rights of the index.php and the directory are ok...so thats the only workaround for my problem untin now

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because the workaround are very ugly, i hope u can find and fix these bugs (i think these are bugs...maybe its my config...i dont know  )

and last but not least i think i get the answer to all these questions. i looks like your component cant handle the seo urls. i used a workaround called "seo without mod_rewrite" so the urls now look like http://www.myurl.org//index.php/component/option,com_smf/Itemid,46/    and not http://www.myurl.org//index.php?option=com_smf&Itemid=46&

thanks very much!!

sorry for my bad bad english