[Zope] ZODB.POSException.ConflictError (in custommade product)

[Gitte Wange]

Hello,

I have created a small tool for CMF to count how many times a specific 
object has been viewed.
It's very simple. It works by a call I have added to my main_template.pt 
that calls the tool with the URL of recent object and counts up by 1.

Now from time to time we see the following error:

Site Error
An error was encountered while publishing this resource.
ZODB.POSException.ConflictError
Sorry, a site error occurred.
Traceback (innermost last):
Module ZPublisher.Publish, line 150, in publish_module
Module Products.Localizer, line 58, in new_publish
Module ZPublisher.Publish, line 127, in publish
Module Products.Localizer, line 58, in new_publish
Module ZPublisher.Publish, line 127, in publish
Module Products.Localizer, line 58, in new_publish
Module ZPublisher.Publish, line 127, in publish
Module Products.Localizer, line 58, in new_publish
Module ZPublisher.Publish, line 122, in publish
Module Zope.App.startup, line 142, in zpublisher_exception_hook
Module ZPublisher.Publish, line 102, in publish
Module Zope.App.startup, line 200, in commit
Module ZODB.Transaction, line 235, in commit
Module ZODB.Transaction, line 349, in _commit_objects
Module ZODB.Connection, line 300, in commit
ConflictError: database conflict error (oid 000000000001c065, class 
Products.CMFCounter.CMFCounterTool.CMFCounterTool)

What is causing this error ??
Have I made some mistakes in the code of my tool ?

Any hints - because the error is really annoying in a production site ;-)

Greetings,
Gitte Wange