To confirm, your mpasm is installed in the directory? For some reason pbp does not see it. Perhaps you need to reinstall mplab ide. When you run mpasm by itself, can you run it from the directory I showed you?

If you look in the pbpmplab.bat file, it shows you where it is going to look. You can even modify it, but you shouldn't need to. What operating system are you using 64 bit, or 32 bit?

Here's where it is going to look:
Code:
@echo off
setlocal enabledelayedexpansion 

:: This file is intended to be run from MPLAB for compilation
:: using the PICBASIC PRO Compiler.  PBPMPLAB.BAT should be
:: located in the PBP install folder (default C:\PBP). 

:: Set for default location on 32-bit systems
SET MPASMWIN_PATH=C:\Program Files\Microchip\MPASM Suite

:: If that doesn't work, set for default location on 64-bit systems
IF NOT EXIST "!MPASMWIN_PATH!\MPASMWIN.EXE" (
SET MPASMWIN_PATH=C:\Program Files ^(x86^)\Microchip\MPASM Suite
)
  
::*************** User modifications here ***************************


:: In order for PBP to launch the MPASMWIN Assembler, the 
:: location of MPASMWIN.EXE will be appended to the existing 
:: PATH  environment variable.  If MPASMWIN is not located in 
:: one of the default folders above, uncomment and change the
:: following line to reflect the true location:

rem   SET MPASMWIN_PATH=C:\Program Files ^(x86^)\Microchip\MPASM Suite