[TYPO3] strange warning while logging into the backend

[Elise Daans]

Hi!

Until now everyting went quite well (i'm a beginner) and i was playing a bit 
with the backend;
But if i log out now en try to login again it goes wrong.
If I typ the wrong password, nothing happens, and that's ok i guess.
If i typ the right password, i get the following warnings and i don't get 
into the backend:

Warning: Failed to Connect in
c:\apache\htdocs\quickstart\typo3\t3lib\class.t3lib_beuserauth.php on line
222

Warning: Cannot add header information - headers already sent by (output
started at
c:\apache\htdocs\quickstart\typo3\t3lib\class.t3lib_beuserauth.php:222) in
c:\apache\htdocs\quickstart\typo3\index.php on line 294

I tried and find out what is wrong but i don't really understand, because of 
no experience.
Can anybody help me out?
btw: If  i login to the intalltool i can reach the backend from there but 
only if i first change the password ... (also quite strange if you ask me)

Many thanks,

Elise