Hmmm... let's see.
Make sure you have the following:
ms0:/SEPlugins (Folder)
ms0:/SEPlugins/piKey.PRX
ms0:/SEPlugins/piKey (Folder)
ms0:/SEPlugins/piKey/CTRLMap.txt
ms0:/SEPlugins/piKey/piKeyConfig.txt
ms0:/SEPlugins/piKey/PSPIRKeyB.ini
ms0:/SEPlugins/piKey/InputDrivers (Folder)
ms0:/SEPlugins/piKey/InputDrivers/piKeySIO.PRX
ms0:/SEPlugins/piKeyInputDrivers/piKeyIR.PRX
ms0:/SEPlugins/piKey/OutputDrivers (Folder)
ms0:/SEPlugins/piKey/OutputDrivers/piKeyCTRLOut.PRX
ms0:/SEPlugins/piKey/OutputDrivers/piKeyOSKOut.PRX
ms0:/SEPlugins/piKey/OutputDrivers/piKeyDanzeffOutOut.PRX
Your PSPIRKeyB.ini should look like this:
# PSPIRKeyB.ini File
#
# This file is to choose your keyboard make/type and it's correct keymap.
# This file ensures that your PSP responds well to your IR keyboard.
#
#
[Keyboard]
#
#
# IR Keyboard Type:
#
Keyboard = 15;
#
# Existing IR keyboard values are:
#
# 0 - No IR Keyboard
# 1 - Compaq / HP Foldable IR Keyboard
# 2 - Snap'n'Type IR Keyboard
# 3 - Belkin F8U1500 IR Keyboard
# 5 - HP Slim IR Keyboard
# 8 - Belkin IR Keyboard (not IrDA)
# 9 - Flexis FX-100 IR Keyboardeyboard
# 10 - Benq G250 IR Gamepad
# 12 - Micro Innovations Foldaway IR Keyboard
# 13 - Micro Innovations IR Datapad
# 14 - Compaq IR Micro Keyboard
# 15 - Targus Universal IR Wireless Keyboard
# 18 - Freedom IR Keyboard
# 19 - NOVAETS - KIS2 - IR Keyboard
# 20 - Palm Universal Wireless IR Keyboard
# 21 - Hama Palm IR Keyboard
# 22 - Sprint PDA Keyboard
#
#
# This is the directory that the keymaps. It's best not to edit this unless
# you fully understand what you are doing.
#
MapFile_Dir = 'ms0:/SEPlugins/piKey/Keymap';
#
# This is the keymap that will be loaded. Make sure you add the .ini extension.
#
Map = 'Targus.ini';
#
#
# Key Repeats:
#
# This feature allows users to get a better feel out of their IR keyboards.
# key repeats allow users hold hold down a key and for it to repeat its' action
# untill it is released.
#
# This is how long you require to hold they key down before it repeats itself:
#
# Set this value to "0" if you don't want key repeats.
#
Delay = 125;
#
# This is the speed of the repeat. It's best to have a value under 1.
#
# Set this value to "0" if you don't want key repeats.
#
Rate = 0.9;
Your CTRLMap.txt should look like this:
# CTRLMap.txt File.
#
# This is the piKey CTRL map. Here is where you set the keys you wish to assign
# to each PSP control.
#
# Please note that not ALL the controls need to be added and that the
# piKeyCTRL.TXT will only read the first 23 commands.
#
# Here are the PSP controls:
#
# Up (D-Pad)
# Down (D-Pad)
# Left (D-Pad)
# Right (D-Pad)
# LTrigger (Left Trigger)
# RTrigger (Right Trigger)
# Start (Face Button)
# Select (Face Button)
# Triangle (Face Button)
# Cross (Face Button)*
# Circle (Face Button)*
# Square (Face Button)
# Analog_Up (Analogue Movement)
# Analog_Down (Analogue Movement)
# Analog_Left (Analogue Movement)
# Analog_Right (Analogue Movement)
# Help (Displays The CTRLMap.TXT Settings)
# Cancel (General Cancel Button - Circle/Triangle)*
# Confirm (General Confirm Button - Circle/Start/Cross)*
#
# *Please note that it's recommended to use Confirm/Cancel instead of
# Cross/Circle.
#
# Keyboard Controls:
#
UP = UP
DOWN = DOWN
LEFT = LEFT
RIGHT = RIGHT
ENTER = CONFIRM
ESC = CANCEL
DELETE = CANCEL
BACKSPACE = CANCEL
HOME = HELP
END = TRIANGLE
PAGEUP = SQUARE
LEFTMETA = HOME
MINUS = LTRIGGER
EQUAL = RTRIGGER
TAB = SELECT
SPACE = START
W = ANALOG_UP
S = ANALOG_DOWN
A = ANALOG_LEFT
D = ANALOG_RIGHT
Your piKeyConfig.txt should look like this:
# piKeyConfig.txt file.
#
# Format:
#
# Lines beginning with # are comments you need to read.
# Other lines are in the format PARAMETER = VALUE.
#
#
# SIO Debugging:
#
# Y = Enable debugging via the headphone serial port.
# N = Disable debugging (recommended).
#
SIO DEBUG = N
#
#
# On-Screen Status Messages:
#
# Y = Display on-screen status messages.
# N = Do not display on-screen status messages (use if it causes problems).
#
STATUS MESSAGES = Y
#
#
# Disabled Plugins:
#
# Plugin names in this list will not be loaded by piKey, even if they're
# present in the plugins folder. You can use this to disable plugins
# without having to delete them. The list is comma-separated, and #
# are case-sensitive.
#
# The SIO plugin is disabled by default. If you choose to enable it, you
# will also need to enable SIO DEBUG above.
#
DISABLED PLUGINS = piKeysio.prx
#
#
# Disable piKey In v1.50 (Homebrew) Mode:
#
# Set to 'Y' to disable piKey in v1.50 (homebrew) mode, even if it has been
# flashed to flash0 to the v1.50 kernel configuration.
#
DISABLED IN 150 = N
#
#
# Hotkey To Disable piKey During Reboot:
#
# If you hold this key down, then piKey will stop itself from loading.
# This is a bitmask from the pspctrl.h constants. Popular choices include:
#
# SELECT: 0x000001
# LTRIGGER + RTRIGGER: 0x000300
# LTRIGGER + SELECT: 0x000101
#
DISABLE HOTKEY = 0x000001
#
#
# Automatic Select Button Presser:
#
# This option allows you to set the amount of times the PSP 'Select'
# key is pressed to ensure you get the correct characters in the
# PSP 'On Screen keyboard'. Please don't edit the values unless you know
# what you are doing. Please note that it isn't possible to have perfect input
# in the URL box and in a text box. You will still have to press the 'Select' key
# but just not as frequently.
#
XMB OSK = 0
#
BROWSER OSK = 0
#
#
You should also have:
ms0:/SEPlugins/Game.txt
ms0:/SEPlugins/Game150.txt
ms0:/SEPlugins/VSH.txt
Inside them you should have:
ms0:/SEPlugins/piKey.PRX
Also in the recovery menu, you should have to following enabled:
piKey.PRX [GAME]
piKey.PRX [GAME150]
piKey.PRX [VSH]
Try it on a cleanmemory card. piKey can sometimes have issues with Lexar and fake cards.
If it still fails, give me an email at:
Unofficial.piKey Support@hotmail.co.ukAnd I'll send you another pack that let's you install it manualy.
Unofficial piKey 0.5 will install better I assure you. The problems happened since the Slim came out.

We'll sort this out!
If you're saying that your keyboard works with PSPWrite, then your keyboard cannot be the issue.

Have a good day!
Angelo