Exception when detaching/serializing a page

[Philipp]

We have been successfully running a Wicket-driven Web application for 
about 6 month now. Since a few days the application keeps giving me 
errors of the following kind:

May 01 09:04:56 
<https://papertrailapp.com/searches/22745?time=1335888296> 
domU-12-31-39-0A-59-A1 ERROR: [Live]: 
org.apache.wicket.Session.requestDetached.1454: Exception when 
detaching/serializing page

May 01 09:05:14 
<https://papertrailapp.com/searches/22745?time=1335888314> 
domU-12-31-39-0A-59-A1 ERROR: [Live]: 
org.apache.wicket.Session.requestDetached.1454: Exception when 
detaching/serializing page

May 01 09:05:15 
<https://papertrailapp.com/searches/22745?time=1335888315> 
domU-12-31-39-0A-59-A1 ERROR: [Live]: 
org.apache.wicket.Session.requestDetached.1454: Exception when 
detaching/serializing page

May 01 09:10:15 
<https://papertrailapp.com/searches/22745?time=1335888615> 
domU-12-31-39-0A-59-A1 ERROR: [Live]: 
org.apache.wicket.Session.requestDetached.1454: Exception when 
detaching/serializing page


The website itself is still being shown, however, modal windows for 
example do not work any more.

I have been googling around for that error for quite a while, but did 
not find any helpful result.

Anybody else already experienced some error like that and can point me 
into a direction where I can further investigate the issue?

Philipp