Reading process memory

[FEARHQ]

While writing a tiny library to read/write process memory I came across a rather unusual problem. While I can write to the process memory without a hitch, I have discovered a wierd bug that would crash the process of which you are reading the memory and I'm not sure why this happens. What I have actually done is use the ToolHelp32 library to traverse the module list and wait until a certain module is loaded (sleeping 10 milliseconds if not found), get it's base address and base size and then proceed to read it's memory with what I have written below. The problem is that the module fails in really odd manners after I try to read it with the code below. My write routine is very similar and produces no faults.

;GetProcessMemory proc uses ecx dwProcessId:DWORD, lpAddress:DWORD, dwSize:DWORD, lpBuffer:DWORD
;	LOCAL hProcess:DWORD
;	LOCAL oldProt:DWORD
;	LOCAL dummyProt:DWORD
;	
;	; Attempt to open the process for write operations
;	invoke OpenProcess, PROCESS_VM_OPERATION+ PROCESS_VM_READ, FALSE, dwProcessId
;	.IF eax == 0
;		ret
;	.endif
;	mov hProcess, eax
;	
;	; Set the page protection to allow read, write and execute status
;	invoke VirtualProtectEx, hProcess, lpAddress, dwSize, PAGE_EXECUTE_READWRITE, addr oldProt
;	or eax, eax
;	jz Failed
;	
;	; Read the target process's memory
;	invoke ReadProcessMemory, hProcess, lpAddress, lpBuffer, dwSize, NULL
;	or eax, eax
;	jz Failed
;	
;	; Restore the old page protection
;	invoke VirtualProtectEx, hProcess, lpAddress, dwSize, oldProt, addr dummyProt
;	or eax, eax
;	jz Failed
;	
;	invoke CloseHandle, hProcess
;	ret
;	
;Failed:
;	invoke CloseHandle, hProcess
;	xor eax, eax
;	ret
;GetProcessMemory endp