OSError: [Errno 22] Invalid argument: when trying to open a file

Question

im trying to open a file, but whenever I open it it returns the error OSError: [Errno 22] Invalid argument:. I have no idea why, I'll show you a bit of my code:

initialdir = pathlib.Path(__file__).parent.absolute()
lockerdir = (str(initialdir) + str('/locker'))
try:
        file = open('openfile.ivd', 'r+')
        mostrecentpath = file.read()
        file.close()
    except:
        print("No files currently open")
        finishedprocess()

    filename = pathlib.Path(mostrecentpath).stem
    print(filename)
    fullfilename = os.path.basename(mostrecentpath)
os.chdir(lockerdir)
        print(filename)
        with open(fullfilename, "rb") as file:
            file_data = file.read()
            encrypted_data = fernet.encrypt(file_data)
            file.close()
        #writes to the binary of a file
        with open(fullfilename, "wb") as file:
            file.write(encrypted_data)
            file.close()
        os.chdir(initialdir)

openfile.ivd already exists. It contains the path of the last file taht was opened by my program. When printing filename I get the output, test, however in my full error I get the error OSError: [Errno 22] Invalid argument: 'test.txt\n'. Any ideas?