Problem with jasper subreport java.io.StreamCorruptedException

I was getting the following error executing my jasper report with a subreport. I am using iReport but it should be similar in other applications.

Error loading object from file  bla bla bla
bla bla bla
bla bla bla
Caused by: java.io.StreamCorruptedException: invalid stream header: 3C3F786D
    at java.io.ObjectInputStream.readStreamHeader(ObjectInputStream.java:783)
    at java.io.ObjectInputStream.<init>(ObjectInputStream.java:280)
    at net.sf.jasperreports.engine.util.JRLoader.loadObject(JRLoader.java:87)
    ... 16 more  

 The problem is that you have to call the .jasper file of the subreport and not the .jrxml