Python Append From Text file outputs error

I am currently testing the third phase of my program, and this errors repeatedly appears throughout the testing of this code below:

I am attempting to read in some values into a dictionary and printing the dictionary to show me the last three scores of each user (I originally chose 4, but I have changed my design idea.) The code is below:

import collections 
from collections import defaultdict 
worker_scores = collections.defaultdict(lambda: collections.deque(maxlen=3))
import operator

with open('score_names.txt') as f:
     for line in f: 
        worker,score = line.split(":")
        worker_scores[worker].append(int(score)) 

for name in sorted(program_scores):
    print(name," ".join(map(str,program_scores[worker])))

The text file is also shown below:

AdamJohnson:10
AdamJohnson:20
AdamJohnson:30
AdamJohnson:40
AdamJohnson:50
AdamJohnson:60 
MichaelJordan:70
MichaelJordan:80
MichaelJordan:90
MichaelJordan:100
DavidSnowman:110
DavidSnowman:120
DavidSnowman:130
DavidSnowman:140

Now, if the text file only included AdamJohnson, as shown:

AdamJohnson:10
AdamJohnson:20
AdamJohnson:30
AdamJohnson:40
AdamJohnson:50
AdamJohnson:60 

Then the IDLE correctly prints:

AdamJohnson 40 50 60

BUT when MichaelJordan and DavidSnowman exist, I want the IDLE TO show:

AdamJohnson 40 50 60
MichaelJordan 80 90 100
MichaelJordan 120 130 140

Yet instead, this error appears:

Traceback (most recent call last):
  File "/Users/Ahmad/Desktop/TESTS/Task 3/Dictionary copy.py", line 8, in <module>
     worker,score = line.split(":")
ValueError: need more than 1 value to unpack

How can I fix this to make sure that the result I want is obtained in the IDLE when printed?

Thanks, Delbert.

UPDATE The code now functions, but the scores are printed incorrectly... see this code:

AdamJohnson 120 130 140
DavidSnowman 120 130 140
MichaelJordan 120 130 140

Why is this happening???