I have found if I try to execute a task with an option that is not recognized I get an internal regX error, here is the output to the console:

C:\Development\webctrl\main\dev>packageDist -Pi4jinst=C:\Program Files\install4j

'packageDist' is not recognized as an internal or external command,
operable program or batch file.

C:\Development\webctrl\main\dev>gradle packageDist -Pi4jinst=C:\Program Files\in
stall4j
Working on webctrl:popup

FAILURE: Build aborted because of an internal error.

• What went wrong:
  Build aborted because of an unexpected internal error. Please file an issue at:
  www.gradle.org.

• Try:
  Run with -d option to get additional debug info.

• Exception is:
  java.util.regex.PatternSyntaxException: Illegal/unsupported escape sequence near
  index 35
  \Q\EFiles[\p {javaLowerCase}\p{Digit}]*\Q\E\install[\p{javaLowerCase}

  \p

  {Digit}

  ]*\
  Q4j\E
  ^
  at java.util.regex.Pattern.error(Pattern.java:1713) [na:1.6.0_17]
  at java.util.regex.Pattern.escape(Pattern.java:2177) [na:1.6.0_17]
  at java.util.regex.Pattern.atom(Pattern.java:1952) [na:1.6.0_17]
  at java.util.regex.Pattern.sequence(Pattern.java:1834) [na:1.6.0_17]
  at java.util.regex.Pattern.expr(Pattern.java:1752) [na:1.6.0_17]
  at java.util.regex.Pattern.compile(Pattern.java:1460) [na:1.6.0_17]
  at java.util.regex.Pattern.<init>(Pattern.java:1133) [na:1.6.0_17]
  at java.util.regex.Pattern.compile(Pattern.java:823) [na:1.6.0_17]
  at org.gradle.util.NameMatcher.getPatternForName(NameMatcher.java:111) [
  gradle-core-0.9-20091221160531-0500.jar:0.9-20091221160531-0500]
  at org.gradle.util.NameMatcher.find(NameMatcher.java:63) [gradle-core-0.
  9-20091221160531-0500.jar:0.9-20091221160531-0500]
  at org.gradle.execution.TaskNameResolvingBuildExecuter.doSelect(TaskName
  ResolvingBuildExecuter.java:102) [gradle-core-0.9-20091221160531-0500.jar:0.9-20
  091221160531-0500]
  at org.gradle.execution.TaskNameResolvingBuildExecuter.select(TaskNameRe
  solvingBuildExecuter.java:41) [gradle-core-0.9-20091221160531-0500.jar:0.9-20091
  221160531-0500]
  at org.gradle.execution.DelegatingBuildExecuter.select(DelegatingBuildEx
  ecuter.java:46) [gradle-core-0.9-20091221160531-0500.jar:0.9-20091221160531-0500
  ]
  at org.gradle.execution.DefaultBuildExecuter.select(DefaultBuildExecuter
  .java:52) [gradle-core-0.9-20091221160531-0500.jar:0.9-20091221160531-0500]
  at org.gradle.GradleLauncher.doBuildStages(GradleLauncher.java:191) [gra
  dle-core-0.9-20091221160531-0500.jar:0.9-20091221160531-0500]
  at org.gradle.GradleLauncher.doBuild(GradleLauncher.java:133) [gradle-co
  re-0.9-20091221160531-0500.jar:0.9-20091221160531-0500]
  at org.gradle.GradleLauncher.run(GradleLauncher.java:103) [gradle-core-0
  .9-20091221160531-0500.jar:0.9-20091221160531-0500]
  at org.gradle.launcher.Main.execute(Main.java:93) [gradle-launcher-0.9-2
  0091221160531-0500.jar:0.9-20091221160531-0500]
  at org.gradle.launcher.Main.main(Main.java:42) [gradle-launcher-0.9-2009
  1221160531-0500.jar:0.9-20091221160531-0500]
  at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) [na:1.6.0
  _17]
  at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.
  java:39) [na:1.6.0_17]
  at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAcces
  sorImpl.java:25) [na:1.6.0_17]
  at java.lang.reflect.Method.invoke(Method.java:597) [na:1.6.0_17]
  at org.gradle.launcher.GradleMain.main(GradleMain.java:51) [gradle-launc
  her-0.9-20091221160531-0500.jar:0.9-20091221160531-0500]

BUILD FAILED

Total time: 10.373 secs

C:\Development\webctrl\main\dev>

In this case the variable should have been written like this -Pi4jinst="C:\Program Files\install4j", this would have worked without issue.