warnings and their meanings and fork in particular...

hi, is there somewhere I can find the possible meaning, (suggested solutions or something like that) to the error msgs and warinings? I am running php4.0.4pl1 on NT4.0 w/ IIS4.0, While trying to delete a file prior to upload i get the following error, i dont understand what it means by "fork", the file to delete is there and what im trying to do is delete the file to the be able to copy a diffrent file in its place (which has the same filename) but it doesnt overwrite the file... Warning: Unable to fork [del d:\home\lineagialla\img\img_colonna1.gif] in D:\home\lineagialla\riservata\index.php on line 177 the code i am reffering to is: system( "del d:\\home\\lineagialla\\img\\img_colonna1.gif" ); copy( $userfile, "d:\\home\\lineagialla\\img\\img_colonna1.gif");