Exception: Prelude.read: no parse - parsing

Question

For an assignment on parser if been working on the following code in Haskell;
Imports;
import ParseLib.Simple
import Prelude hiding ((<*>), (<$>),(<$),(<*))
import Data.Char
import Data.Time.Calendar hiding (Day)
Data Types;
data DateTime = DateTime { date :: Date
, time :: Time
, utc :: Bool }
deriving (Eq, Ord)
data TimeUTC = Eps | Z deriving Show
data Date = Date { year :: Year
, month :: Month
, day :: Day }
deriving (Eq, Ord)
newtype Year = Year { unYear :: Int } deriving (Eq, Ord)
newtype Month = Month { unMonth :: Int } deriving (Eq, Ord)
newtype Day = Day { unDay :: Int } deriving (Eq, Ord)
data Time = Time { hour :: Hour
, minute :: Minute
, second :: Second }
deriving (Eq, Ord)
newtype Hour = Hour { unHour :: Int } deriving (Eq, Ord)
newtype Minute = Minute { unMinute :: Int } deriving (Eq, Ord)
newtype Second = Second { unSecond :: Int } deriving (Eq, Ord)
data Result = SyntaxError | Invalid DateTime | Valid DateTime deriving (Eq, Ord)
instance Show DateTime where
show = printDateTime
instance Show Result where
show SyntaxError = "date/time with wrong syntax"
show (Invalid _) = "good syntax, but invalid date or time values"
show (Valid x) = "valid date: " ++ show x
With show instances for all the newtypes equel to this;
instance Show Year where
show (Year a) = show a
The parsers look like this;
-- Exercise 1
parseDateTime :: Parser Char DateTime
parseDateTime = DateTime <$> parseDate <*> parseTime <*> parseUTC
parseDigits :: Int -> Parser Char Int
parseDigits n (xs) | length f == n = [(read f :: Int, drop n xs)]
| otherwise = []
where f = take n xs
-- Time parsing
parseTime :: Parser Char Time
parseTime = Time <$> parseHour <*> parseMinute <*> parseSeconds
parseHour :: Parser Char Hour
parseHour xs | length (checkT) == 2 = [(Hour(read f :: Int), (drop 3 xs))]
| length (checkT) == 3 = [(Hour(read f :: Int), (drop 2 xs))]
| otherwise = []
where f = take 3 xs
checkT = if (head f) == 'T' then drop 1 f else f
parseMinute :: Parser Char Minute
parseMinute = Minute <$> (parseDigits 2)
parseSeconds :: Parser Char Second
parseSeconds = Second <$> (parseDigits 2)
-- Date parsing
parseDate :: Parser Char Date
parseDate = Date <$> parseYear <*> parseMonth <*> parseDay
parseYear :: Parser Char Year
parseYear = Year <$> (parseDigits 4)
parseMonth :: Parser Char Month
parseMonth = Month <$> (parseDigits 2)
parseDay :: Parser Char Day
parseDay = Day <$> (parseDigits 2)
-- UTC parsing
parseUTC :: Parser Char Bool
parseUTC = utcToBool <$> (option ((\a -> Z) <$> satisfy (=='Z')) Eps)
utcToBool :: TimeUTC -> Bool
utcToBool Eps = False
utcToBool Z = True
-- Exercise 2
isFinished :: [(a, [b])] -> Maybe a
isFinished [] = Nothing
isFinished ((result, rest):xs) | null rest = Just result
| otherwise = isFinished xs
run :: Parser a b -> [a] -> Maybe b
run p s = isFinished r
where r = p s
-- Exercise 3
printDateTime :: DateTime -> String
printDateTime (DateTime (Date year month day)(Time hour minute second)timezone) = f year 4 ++ f month 2 ++ f day 2 ++ "T" ++ f hour 2 ++ f minute 2 ++ f second 2 ++ endOrZ timezone
where f s a = take (a - length (show s)) (repeat '0') ++ show s
endOrZ False = ""
endOrZ True = "Z"
-- Exercise 4
parsePrint s = fmap printDateTime $ run parseDateTime s
So now my problem. After finishing exercise 4 we are supossed to test "parsePrint" and if the string that goes in is correct it returns Just "inputstring" else nothing
So i tried to test it with some strings that were given to us and i got the following error;
*Main> parsePrint "20111012T083945"
*** Exception: Prelude.read: no parse
Just "20111012T*Main>
Now I found some thread on here about the same error, these were mostly about missing qoutes and one about the read instance. Yet I'm still not really able to figure out the problem.
I don't expect the flat out answser seeing it's for a school assignment but if someone could point me in the right direction I would be really grateful, seeing I've been trying to figure it out for a couple of hours now.
-- Indents got a bit messed up when I copied the code here, but I don't think that would be the problem.