CoreServicesUIAgent quit unexpectedly ??

Someone please help.

I am getting the message "CoreServicesUIAgent quit unexpectedly" over and over. I am a novice and don't know what this means, so please assume I know nothing.
I believe this began occurring after I removed my "Prokit.framework" file, as described here:http://reviews.cnet.com/8301-13727_7-20096767-263/a-fix-for-logic-crashing-in-snow-leopard/
I downloaded the latest ProKit 7.0 framework file, but it wouldn't open after I downloaded it. After trying repeatedly, I decided to take the original file back out of the trash and put it back were it was. I'm pretty sure that's when my problems began.
Let me emphasize, I don't have any ideal what these files are for or what they do, so if you can help me please explain as if you were talking to a complete novice.
I'm guessing this will be a simple fix if I someone can simply tell me what I did wrong.
Many thanks in advance.
A fellow Mac user in need of support.

Crash Report

WZZZ - thanks for the reply. The crash report is below. One thing that triggers the error is when I attempt to open files attached to an email, such as an Excel file. I double click it, get the spinning color wheel for about 10 second, and get a message saying the file isn't recognized and I am prompted to select an application to open it. I found that I can only open the file after opening Excel first and then selecting it. Here's the crash report - Process: CoreServicesUIAgent [41319]
Path: /System/Library/CoreServices/CoreServicesUIAgent.app/Contents/MacOS/CoreServicesUIAgent
Identifier: CoreServicesUIAgent
Version: ??? (???)
Code Type: X86-64 (Native)
Parent Process: launchd [131]

Date/Time: 2012-11-07 18:00:44.283 -0500
OS Version: Mac OS X 10.7.4 (11E53)
Report Version: 9

Anonymous UUID: B19F4ED2-CDEC-4293-A41F-C029B6DF546A

Crashed Thread: 0

Exception Type: EXC_BREAKPOINT (SIGTRAP)
Exception Codes: 0x0000000000000002, 0x0000000000000000

Application Specific Information:
dyld: launch, loading dependent libraries

Dyld Error Message:
Library not loaded: /System/Library/PrivateFrameworks/PackageKit.framework/Versions/A/PackageKit
Referenced from: /System/Library/CoreServices/CoreServicesUIAgent.app/Contents/MacOS/CoreServicesUIAgent
Reason: image not found

Binary Images:
0x10a969000 - 0x10a97bff7 com.apple.coreservices.uiagent (61.11 - 61.11) <D6EE23A9-D02D-30F4-9E6A-A2FA21B0583E> /System/Library/CoreServices/CoreServicesUIAgent.app/Contents/MacOS/CoreServicesUIAgent
0x10a98a000 - 0x10a99cff7 libbsm.0.dylib (??? - ???) <349BB16F-75FA-363F-8D98-7A9C3FA90A0D> /usr/lib/libbsm.0.dylib
0x10a9ab000 - 0x10ac94ff7 com.apple.security (7.0 - 55148.1) <E9C46204-1336-3D90-BC67-5162FC7079D2> /System/Library/Frameworks/Security.framework/Versions/A/Security
0x7fff6a569000 - 0x7fff6a59dbaf dyld (195.6 - ???) <C58DAD8A-4B00-3676-8637-93D6FDE73147> /usr/lib/dyld

Model: MacBookPro8,2, BootROM MBP81.0047.B27, 4 processors, Intel Core i7, 2.2 GHz, 16 GB, SMC 1.69f3
Graphics: AMD Radeon HD 6750M, AMD Radeon HD 6750M, PCIe, 512 MB
Graphics: Intel HD Graphics 3000, Intel HD Graphics 3000, Built-In, 512 MB
Memory Module: BANK 0/DIMM0, 8 GB, DDR3, 1333 MHz, 0x859B, 0x435438473353313333394D2E4D3136464544
Memory Module: BANK 1/DIMM0, 8 GB, DDR3, 1333 MHz, 0x859B, 0x435438473353313333394D2E4D3136464544
AirPort: spairport_wireless_card_type_airport_extreme (0x14E4, 0xD6), Broadcom BCM43xx 1.0 (5.106.198.4.20)
Bluetooth: Version 4.0.5f11, 2 service, 18 devices, 1 incoming serial ports
Network Service: Wi-Fi, AirPort, en1
Serial ATA Device: Hitachi HTS545050B9A302, 500.11 GB
Serial ATA Device: MAT****ADVD-R UJ-8A8
USB Device: FaceTime HD Camera (Built-in), apple_vendor_id, 0x8509, 0xfa200000 / 3
USB Device: hub_device, 0x0424 (SMSC), 0x2513, 0xfa100000 / 2
USB Device: BRCM2070 Hub, 0x0a5c (Broadcom Corp.), 0x4500, 0xfa110000 / 5
USB Device: Bluetooth USB Host Controller, apple_vendor_id, 0x821a, 0xfa113000 / 7
USB Device: Apple Internal Keyboard / Trackpad, apple_vendor_id, 0x0252, 0xfa120000 / 4
USB Device: hub_device, 0x0424 (SMSC), 0x2513, 0xfd100000 / 2
USB Device: IR Receiver, apple_vendor_id, 0x8242, 0xfd110000 / 3