Tainted strings are new in Zope 2.6 to make it more difficult that cross scripting bugs slip in.
If you are lucky, there is an explicite conversion between a tainted string and a string. If not, you must make one in an External Method.
Thanks for your reply. I just found this thread about TaintedStrings: http://mail.zope.org/pipermail/zope-coders/2002-August/001598.html and my case was exposed there:
Passing a TaintedString value from a DTML template to other objects such as Python code, External Methods, Python Scripts, etc, may cause them to break because they did not anticipate a TaintedString object.
Actually my case it's really uncommon, but as you see it can happen: one of the users wanted to say that the dimmensions of something should be minor than 1 m, so he wrote "< 1 m". Then come that exception. One possible solution could be to convert all the "<" symbols to "<". But I was wondering if there is another way of dealing with this TaintedStrings (appart of disabling the check, off course). Regards, Josef