TypeError while checking for permissions with os.access() on windows xp

[ryniek90]

I've got some code that checks priviliges on two paths:
First - chosen by user
Second - hardcoded home directory represented by **os.getenv('HOME')** - 
(os.getenv('HOME') works both on Linux and Windows)

Here's the code:
"
def __check_set_perm(self, rd_obj_path, backup_dest):

        try:

            if os.path.exists(rd_obj_path):
                if os.access(rd_obj_path, os.R_OK) != True:
                    print "Have no permissions on [%s] for reading 
operation.\nTrying to set them..." % os.path.split(rd_obj_path)[1]
                    if not os.path.isdir(rd_obj_path):
                        os.chmod(rd_obj_path, stat.S_IREAD)
                    else:
                        for root, dirs, files in os.walk(rd_obj_path):
                            for f in files:
                                os.chmod(os.path.join(root, f), 
stat.S_IREAD)
                    print "Get permissions for reading on [%s] 
successfully." % os.path.split(rd_obj_path)[1]
                else:
                    print "Have permissions on [%s] for reading." % 
os.path.split(rd_obj_path)[1]

                if os.access(backup_dest, os.W_OK) != True:
                    print "Have no permissions on [%s] for writing 
operation.\nTrying to set them..." % os.path.split(backup_dest)[1]
                    os.chmod(backup_dest, stat.S_IWRITE)
                    print "Get permissions for reading on [%s] 
successfully." % os.path.split(backup_dest)[1]
                else:
                    print "Have permissions on [%s] for writing." % 
os.path.split(backup_dest)[1]
            else:
                return "Can't find specified path - [%s]." % rd_obj_path
                sys.exit(0)

        except (Except), ex:
            return ex
"


This code is part of my backup script. When script checks for reading 
permission on 'user chosen path' it seems ok, but when it checks for 
writing permissions on 'home directory', (this line: **if 
os.access(backup_dest, os.W_OK) != True**), i get error:
**TypeError: coercing to Unicode: need string or buffer, NoneType found**
The second os.access check fails, but don't know why. When i turned 
os.W_OK to integer, i get the same error.
But when changed os.W_OK or that int to string, i get error that integer 
is required. I'm launching this code on WinXP Prof+SP3, on Administrator 
account. Is it bug in os.acces() or my code is written wrong?
Btw. i kow that os.chmod in windows can set only read-olny flag, so 
later i'll change the line with **os.chmod(path, stat.S_IWRITE)**

Thanks and cheers.