Hi,here I got a problem when I try to upload file in php4 script. The form is here(exactly) below:

*************************
	<form method=post name="Upload" enctype="multipart/form-data">
	<INPUT TYPE="hidden" name="MAX_FILE_SIZE" value="102400">
	<B>upload file:</B><br>
            local file:
		<INPUT NAME="userfile" TYPE="file" onBlur="serverFileName()"><br>
		remote file:<br> 
		<INPUT NAME="fn" type="text" select() onBlur="validateFileEntry(this.value, this)">
		<input type=hidden name="action" value="upload">
	<input type="submit" value="upload" >
	</form>
***************************

Well,this form works well if I just upload file using the php script which contains the form.
That script also contains other functions to delete,rename,create and edit file and directory. It's something like this:

somephp.php?action=deletefile&filename=filename.ext

Click that url, script will delete a file named "filename.ext" using unlink() function, this is also done perfectly. 
But after that, the upload function doesn't work any more! I will see the variable $action 's value is still "deletefile" but not "upload" after pushed the upload button in that form.
I'm using seesion at the same time , but it never changes the $action 's value, even never read value from it.
Other forms without this line
   enctype="multipart/form-data"
work perfectly.
Could you tell me why?