Error message

Hi,
 
I have a Jahia 4.0.6 running in a Server with the next environment:
 
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WebSphere Platform 5.1 [JDK 1.4.2 ca1420-20040626] [ND 5.1.1 a0426.01] [BASE
5.1.1.2 cf20446.02]  
 
Host Operating System is AIX, version 5.2

Java version = J2RE 1.4.2 IBM AIX build ca1420-20040626 (JIT enabled: jitc),
Java Compiler = jitc, Java VM name = Classic VM
--------------------------------------------------
 
I have this error in my log several times:
 
[11/3/05 17:30:28:018 CET] 1ad378fa DRSCacheApp  E DRSW0008E: Exception is:
java.io.NotSerializableException:
org.jahia.services.usermanager.UserProperties

And this error several times as well:
 
[11/3/05 17:30:28:233 CET] 1ad378fa TraceNLS u No message text associated
with key WARNING:.Cannot.set.header..Response.already.committed. in bundle
com.ibm.ejs.resources.seriousMessages
[11/3/05 17:30:28:233 CET] 1ad378fa SRTServletRes W WARNING: Cannot set
header. Response already committed.
 
Does anybody know the reason for these errors? Your helping will be very
welcomed.
 
Regards.
 
Alex.