[Silva-general] Problems moving a Silva 1.4.2 site from Zope 2.7.x to Zope 2.8.x

[Nico Grubert]

Dear Silva developers,

I am trying to move a Silva 1.4.2 site from Zope 2.7.4. to Zope 2.8.8.
If I try to view the Silva site on Zope 2.8.8. I get the following error:

-----------------------------------------------------------------------
Exception Type  	TypeError
Exception Value 	unbound method __str__() must be called with Image 
instance as first argument (got nothing instead)

Traceback (innermost last):

     * Module ZPublisher.Publish, line 114, in publish
     * Module ZPublisher.mapply, line 88, in mapply
     * Module ZPublisher.Publish, line 40, in call_object
     * Module Shared.DC.Scripts.Bindings, line 311, in __call__
     * Module Shared.DC.Scripts.Bindings, line 348, in _bindAndExec
     * Module Products.PythonScripts.PythonScript, line 323, in _exec
     * Module None, line 17, in index_html
       <PythonScript at /intranet/index_html>
       Line 17
     * Module Shared.DC.Scripts.Bindings, line 311, in __call__
     * Module Shared.DC.Scripts.Bindings, line 348, in _bindAndExec
     * Module Products.PageTemplates.ZopePageTemplate, line 256, in _exec
     * Module Products.PageTemplates.PageTemplate, line 104, in pt_render
       <ZopePageTemplate at /intranet/content.html>
     * Module TAL.TALInterpreter, line 206, in __call__
     * Module TAL.TALInterpreter, line 250, in interpret
     * Module TAL.TALInterpreter, line 711, in do_useMacro
     * Module TAL.TALInterpreter, line 250, in interpret
     * Module Products.Silva.monkey, line 31, in 
silva_do_insertStructure_tal
     * Module DocumentTemplate.ustr, line 44, in ustr

TypeError: unbound method __str__() must be called with Image instance 
as first argument (got nothing instead)
-----------------------------------------------------------------------

I tried to upgrade to Silva 1.5.6 but I get the same error.

Any idea, what's wrong here?

Regards,
    Nico