serialization exception

Hi,

while transforming with xalan this error comes up now and then with large
data source.

java.io.NotSerializableException:
org.apache.xalan.extensions.ExtensionNamespacesManager
 at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1278)

XSL has some java calls and uses few functions as number,translate..

Any reasons for this error?

Thanks,
Shadab