ZipImportError: can't find module

[loial]

I am suddenly having a problem with importing a module from a zip file in Python 2.4.1

What has been working for years suddenly has an error :

zipimport.ZipImportError: can't find module 'mymodule'

PYTHONPATH is correct, it points to the zip file containing mymodule

N.B. the python script(unchanged) is called from a shell script using

python myscript.py

The python script also has a shebang line that references the 2.4.1 install of Python.

Debugging the script shows that PYTHONPATH is set correctly, it points to the zip file containing mymodule

Any ideas?

Platform is Solaris 10