Grok parse error when using custom pattern definitions - regex

Question

I'm trying to use a grok filter in logstash version 1.5.0 to parse several fields of data from a log file.
I'm able to parse a simple WORD field with no issues, but when I try to define a custom pattern and add that in as well, the grok parse fails.
I've tried using a couple of grok debuggers which have been recommended elsewhere to find an issue:
http://grokconstructor.appspot.com/do/match
and
http://grokdebug.herokuapp.com/
both say that my regex should be fine, and return the fields that I want, but when I add it to my logstash.conf, grok fails to parse the log line and simply passes through the raw data to elasticsearch.
My sample line is as follows:
APPERR [2015/06/10 11:28:56.602] C1P1405 S39 (VPTestSlave002_001)| 8000B Connect to CGDialler DB (VPTest - START)| {39/A612-89A0-A598/60B9-1917-B094/9E98F46E} Failed to get DB connection: SQLConnect failed. 08001 (17) [Microsoft][ODBC SQL Server Driver][DBNETLIB]SQL Server does not exist or access denied.
My logstash.conf grok config looks like this:
grok
{
patterns_dir => ["D:\rt\Logstash-1.5.0\bin\patterns"]
match => {"message" => "%{WORD:LogLevel} \[%{KERNELTIMESTAMP:TimeStamp}\]"}
}
and the contents of my custom pattern file are:
KERNELTIMESTAMP %{YEAR}/%{MONTHNUM}/%{MONTHDAY} %{HOUR}:?%{MINUTE}(?::?%{SECOND})?%{ISO8601_TIMEZONE}?
I am expecting this to return the following set of data:
{
"LogLevel": [
[
"APPERR"
]
],
"TimeStamp": [
[
"2015/06/10 11:28:56.602"
]
],
"YEAR": [
[
"2015"
]
],
"MONTHNUM": [
[
"06"
]
],
"MONTHDAY": [
[
"10"
]
],
"HOUR": [
[
"11",
null
]
],
"MINUTE": [
[
"28",
null
]
],
"SECOND": [
[
"56.602"
]
],
"ISO8601_TIMEZONE": [
[
null
]
]
}
Can anyone tell me where my issue is?