Recurring error - Zend controller error

I have started getting this error when modifying items. (I've modified hundreds of them with no problems and now this error pops up every 5 or 6 items.) Backing up and resubmitting the form seems to rectify the situation so this is more of a big annoyance rather than a showstopper.

FYI,

- dave

Omeka Has Encountered an Error
Zend_Controller_Dispatcher_Exception:
Invalid controller specified (admin)
Backtrace:
#0 /home/maynardhistory/collection/application/libraries/Zend/Controller/Front.php(946): Zend_Controller_Dispatcher_Standard->dispatch(Object(Zend_Controller_Request_Http), Object(Zend_Controller_Response_Http))
#1 /home/maynardhistory/collection/application/libraries/Zend/Application/Bootstrap/Bootstrap.php(77): Zend_Controller_Front->dispatch()
#2 /home/maynardhistory/collection/application/libraries/Zend/Application.php(358): Zend_Application_Bootstrap_Bootstrap->run()
#3 /home/maynardhistory/collection/index.php(18): Zend_Application->run()
#4 {main}