I suspect this is not related to the Zend Optimizer bug, but just in case, have you tried following the solutions suggested on that page (i.e. either applying the patch or disabling Zend Optimizer)? Did you try adding the ini_set statement above?
Also double-check to make sure that your cache directory, particularly the t_compile subdirectory and its contents, can be written to by the web server. Using the -R option to chmod and chown is the best way to do this (on a *NIX platform).
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