[wp-hackers] "Plugin could not be activated because it triggered a fatal error." But what is the error?

[Andrew Nacin]

James mentioned to me he was running 2.9.2. I've looked into this further,
and the issue appears to be that we only started including E_COMPILE_ERROR
in default error reporting (including the plugin activation sandbox) in 3.0.
Additionally, we previously overrode the error reporting level set up via
WP_DEBUG in the sandbox. (In 3.0, we account for WP_DEBUG.) Thus, my guess
is you have another plugin that is defining widget(), which throws the
apparently unreported Zend error.