Narrative:

As we approached our cruising altitude of 33000' the cabin altitude warning horn sounded. The cabin altitude was 10000'+, both packs were operating in a normal confign. We declared an emergency (squawked 7700) and started our descent. The F/a's and passenger were briefed. Using both the manual and standby systems, we regained control of the system. A VFR approach and landing were made at mco. The pressurization controller (plus one other part) were replaced.

Google
 

Original NASA ASRS Text

Title: ACR MLG DEVELOPED PRESSURIZATION CONTROL PROBLEM AT CRUISE ALT. EMERGENCY DECLARED.

Narrative: AS WE APCHED OUR CRUISING ALT OF 33000' THE CABIN ALT WARNING HORN SOUNDED. THE CABIN ALT WAS 10000'+, BOTH PACKS WERE OPERATING IN A NORMAL CONFIGN. WE DECLARED AN EMER (SQUAWKED 7700) AND STARTED OUR DSCNT. THE F/A'S AND PAX WERE BRIEFED. USING BOTH THE MANUAL AND STANDBY SYSTEMS, WE REGAINED CONTROL OF THE SYSTEM. A VFR APCH AND LNDG WERE MADE AT MCO. THE PRESSURIZATION CTLR (PLUS ONE OTHER PART) WERE REPLACED.

Data retrieved from NASA's ASRS site as of August 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.