Exception when trying to upgrade GWT 1.5.3 to 1.7.0

I have been trying to upgrade some existing code to use GWT 1.7.0
instead of 1.5.3. Unfortunately I am getting the following exception.
Can anyone give me any advice about what this bug means and how to
identify the cause of the problem?

   Worker permutation 0 of 10
      [ERROR] An internal compiler exception occurred
com.google.gwt.dev.jjs.InternalCompilerException: Could not find
property compil
er.max.vars.per.var
        at
com.google.gwt.dev.js.JsBreakUpLargeVarStatements.getMaxVarsPerStatem
ent(JsBreakUpLargeVarStatements.java:91)
        at com.google.gwt.dev.js.JsBreakUpLargeVarStatements.<init>
(JsBreakUpLar
geVarStatements.java:51)
        at com.google.gwt.dev.js.JsBreakUpLargeVarStatements.exec
(JsBreakUpLarge
VarStatements.java:41)
        at
com.google.gwt.dev.jjs.JavaToJavaScriptCompiler.compilePermutation(Ja
vaToJavaScriptCompiler.java:203)
        at com.google.gwt.dev.CompilePerms.compile(CompilePerms.java:
181)
        at com.google.gwt.dev.ThreadedPermutationWorkerFactory
$ThreadedPermutati
onWorker.compile(ThreadedPermutationWorkerFactory.java:47)
        at com.google.gwt.dev.PermutationWorkerFactory$Manager
$WorkerThread.run(
PermutationWorkerFactory.java:72)
        at java.lang.Thread.run(Thread.java:619)
Caused by: com.google.gwt.core.ext.BadPropertyValueException: Missing
property '
compiler.max.vars.per.var' was not specified
        at com.google.gwt.dev.cfg.StaticPropertyOracle.getPropertyValue
(StaticPr
opertyOracle.java:78)
        at
com.google.gwt.dev.js.JsBreakUpLargeVarStatements.getMaxVarsPerStatem
ent(JsBreakUpLargeVarStatements.java:89)
        ... 7 more
      [ERROR] Unrecoverable exception, shutting down
com.google.gwt.core.ext.UnableToCompleteException: (see previous log
entries)
        at
com.google.gwt.dev.jjs.JavaToJavaScriptCompiler.logAndTranslateExcept
ion(JavaToJavaScriptCompiler.java:609)
        at
com.google.gwt.dev.jjs.JavaToJavaScriptCompiler.compilePermutation(Ja
vaToJavaScriptCompiler.java:212)
        at com.google.gwt.dev.CompilePerms.compile(CompilePerms.java:
181)
        at com.google.gwt.dev.ThreadedPermutationWorkerFactory
$ThreadedPermutati
onWorker.compile(ThreadedPermutationWorkerFactory.java:47)
        at com.google.gwt.dev.PermutationWorkerFactory$Manager
$WorkerThread.run(
PermutationWorkerFactory.java:72)
        at java.lang.Thread.run(Thread.java:619)
   [ERROR] Not all permutation were compiled , completed (0/10)

WARNING: 'com.google.gwt.dev.GWTCompiler' is deprecated and will be
removed in a
 future release.
Use 'com.google.gwt.dev.Compiler' instead.
(To disable this warning, pass -Dgwt.nowarn.legacy.tools as a JVM
arg.)

[INFO]
------------------------------------------------------------------------
[ERROR] BUILD ERROR
[INFO]
------------------------------------------------------------------------
[INFO] WARNING: 'com.google.gwt.dev.GWTCompiler' is deprecated and
will be remov
ed in a future release.
Use 'com.google.gwt.dev.Compiler' instead.
(To disable this warning, pass -Dgwt.nowarn.legacy.tools as a JVM arg.)
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