servlet 与applet通讯错误，请问

I write a little program to check the pipe between applet and servlet ,
I use a button and label. I send the Label (lab.getText()) ,then the server reverse the word back.
when i click the button .I find the errors
the server:
error: java.lang.IllegalStateException: Writer is already being used for this requesterror: java.io.EOFExceptionthe client:
error happened: java.io.StreamCorruptedException: invalid stream headerwhat happened?
thanks in advance!