Can anybody help with this Wordpress intalation error?

I get this error.

Warning: array_merge() [function.array-merge]: Argument #2 is not an array in ..../wp-includes/classes.php on line 324

I guess I need to change something in classes.php?
1) what to what?
2) i can't see numeration of lines, it's all some abracadabra for me

Are you using an older theme? It may not be compatible with your version of wordpress. Or maybe your wordpress is not up to date?

To see line numbers, copy/paste the php into a php editor.

You probably have a plugin that is filtering out headers via the 'nocache_headers' filter. Try deactivating plugins one-by-one until the error goes away; then you'll know which is the culprit.