Help "unfortunately, the process com.android.systemui has stopped" but only in portrait mode..

[Ford Sarnmenington]

Ok - here's one: my Samsung Galaxy S3 has just recently begun showing the "unfortunately, the process com.android.systemui has stopped" each and every time I hold the home key to enter the recent apps screen BUT only if I'm holding the phone in portrait mode. If I turn the phone to landscape mode, the error doesn't occur and I reach the recent apps screen just fine. I am flummoxed. I've tried the "wipe cache partition" option with no success. Any suggestions on what could be happening?