Receiving an AttributeError all of a sudden

I have a block of code which choose a word from a list and displays it on a label and the user has to retype it correctly to move on.

import random
try:
    import tkinter as tk
except ImportError:
    import Tkinter as tk

WORDS = ['Games', 'Development', 'Keyboard', 'Speed', 'Typer', 'Anything',
         'Alpha']
score = 0

def choose_word():
    global word
    entry.focus_set()
    word = random.choice(WORDS)
    label.config(text=str(word.lower()))

def check_entry(event):
    global score
    if entry.get().lower() == word.lower():
        score += 1
        print(score)
    elif entry.get().lower() != word.lower():
        score -= 1
        print(score)
    choose_word()
    entry.delete(0, tk.END)

root = tk.Tk()

label = tk.Label(root)
entry = tk.Entry(root)

label.pack()
entry.pack()

choose_word()
root.bind('<Return>', check_entry)
root.mainloop()

I've been using this same code throughout ALL versions of my code since I started working on it a few months ago. I haven't altered it one bit and it's worked perfectly up until now. The error is:

Exception in Tkinter callback
Traceback (most recent call last):
  File "C:\Users\ernxs\AppData\Local\Programs\Python\Python35-32\lib\tkinter\__init__.py", line 1549, in __call__
    return self.func(*args)
  File "C:\Users\ernxs\Downloads\speedtypr\Speedtypr FINAL\speedtyper.pyw", line 685, in choose_word
    label.config(text=str(word.lower()))
AttributeError: 'generator' object has no attribute 'lower'

I noticed this error last week as it occurred rarely but now I can't get past the first word without it throwing this error. My code has gone through MAJOR changes throughout the past months but I have left these functions and anything related to them completely untouched and I have no idea why it worked perfectly for 3 months then has now stopped working.

I've tried the above code and it works perfectly but when I run it inside my full program I get the error despite nothing else being related to the functions I mentioned.

I've tried included even more of my program (which I hope is not too much) but it still won't throw the same error:

try:
    import tkinter as tk

except ImportError:
    import Tkinter as tk

import time
import random

correct_words = []
WORDS = ['Basic', 'Christmas', 'Summer', 'Sports', 'Winter', 'Negative',
         'Beach', 'Country', 'Christmas', 'Food', 'Games', 'Music', 'Family']

time_score = 0 
word_count = 0
max_words = 12
skips = 0
total_words = 0
words_found = 0

def end_game():
    root.destroy()
def choose_word():
    global word, start_time
    go_btn.pack_forget()
    start_time = time.time()
    entry.focus_set()
    if word_count < max_words:

        word = random.choice(WORDS)

        label.config(text=str(word.lower()))
        time_score_label.config(text="Time: " + str(time_score) + "s")      

    else:
        end_game()

def check_entry(event):
    if entry.get().lower() == word.lower():
        update_right()

    elif entry.get().lower() != word.lower():
        update_wrong()

    if len(entry.get()) < 1:
        update_skip()

    update_time()    
    choose_word()
    entry.delete(0, tk.END)

def update_time():
    global time_score
    time_score += time.time() - start_time
    time_score = round(time_score,2)

def update_skip():
    global skips
    skips += 1
    skip_counter.config(text="Skips: " + str(skips))
    wrong_label.config(text="SKIPPED!", fg='red')
    time_score_label.config(text="Time: " + str(time_score) + "s")

def update_right():
    global word_count, words_found

    word_count += 1
    words_found += 1
    WORDS.remove(word)
    correct_words.append(word)

    time_score_label.config(text="Time: " + str(time_score) + "s")
    word_counter.config(text="Words: " + str(word_count))
    wrong_label.config(text="")

def update_wrong():    
    wrong_label.config(text="WRONG!", fg='red')
    time_score_label.config(text="Time: " + str(time_score) + "s")

def display():
    for i in (label, time_score_label, word_counter, skip_counter, wrong_label,
        entry):
        i.pack()
    choose_word()

root = tk.Tk()
go_btn = tk.Button(root, text="GO!", command=display, width=17)
go_btn.pack()
label = tk.Label(root, font=("Helvetica", 60))
time_score_label = tk.Label(root, text="Time: " + str(time_score) +
                                "s", font=('Helvetica', 14))
word_counter = tk.Label(root, text="Words: " + str(word_count),
                            font =("Helvetica", 14))
skip_counter = tk.Label(root, text="Skips: " + str(skips),
                            font =("Helvetica", 14))
wrong_label = tk.Label(root, text="", font =("Helvetica, 14"))
entry = tk.Entry()

root.bind("<Return>", check_entry)
root.mainloop()

This is everything related to this function and I can't reproduce the error. I won't post my full program since it is way too long so is there anything else I can try?