After upgrading to 2.7 from 2.6.1, I noticed that several of my jobs were not showing up in my Jenkins dashboard.
Looking at jenkins.err.log shows this:

SEVERE: Failed Loading job <JOBNAME>

hudson.util.IOException2: Unable to read <PATH_TO_JOB>\config.xml
at hudson.XmlFile.read(XmlFile.java:137)
at hudson.model.Items.load(Items.java:114)
at jenkins.model.Jenkins$14.run(Jenkins.java:2357)
at org.jvnet.hudson.reactor.TaskGraphBuilder$TaskImpl.run(TaskGraphBuilder.java:146)
at org.jvnet.hudson.reactor.Reactor.runTask(Reactor.java:259)
at jenkins.model.Jenkins$5.runTask(Jenkins.java:798)
at org.jvnet.hudson.reactor.Reactor$2.run(Reactor.java:187)
at org.jvnet.hudson.reactor.Reactor$Node.run(Reactor.java:94)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
Caused by: com.thoughtworks.xstream.converters.ConversionException: null : null
---- Debugging information ----
cause-exception : java.lang.NullPointerException
cause-message : null
class : hudson.model.FreeStyleProject
required-type : com.michelin.cio.hudson.plugins.maskpasswords.MaskPasswordsBuildWrapper
path : /project/buildWrappers/com.michelin.cio.hudson.plugins.maskpasswords.MaskPasswordsBuildWrapper
line number : 175
-------------------------------

at com.thoughtworks.xstream.core.TreeUnmarshaller.convert(TreeUnmarshaller.java:89)
at com.thoughtworks.xstream.core.AbstractReferenceUnmarshaller.convert(AbstractReferenceUnmarshaller.java:63)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:76)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:60)
at com.thoughtworks.xstream.converters.collections.AbstractCollectionConverter.readItem(AbstractCollectionConverter.java:71)
at hudson.util.CopyOnWriteList$ConverterImpl.unmarshal(CopyOnWriteList.java:193)
at hudson.util.DescribableList$ConverterImpl.unmarshal(DescribableList.java:245)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convert(TreeUnmarshaller.java:82)
at com.thoughtworks.xstream.core.AbstractReferenceUnmarshaller.convert(AbstractReferenceUnmarshaller.java:63)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:76)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:60)
at hudson.util.RobustReflectionConverter.unmarshalField(RobustReflectionConverter.java:290)
at hudson.util.RobustReflectionConverter.doUnmarshal(RobustReflectionConverter.java:233)
at hudson.util.RobustReflectionConverter.unmarshal(RobustReflectionConverter.java:180)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convert(TreeUnmarshaller.java:82)
at com.thoughtworks.xstream.core.AbstractReferenceUnmarshaller.convert(AbstractReferenceUnmarshaller.java:63)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:76)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:60)
at com.thoughtworks.xstream.core.TreeUnmarshaller.start(TreeUnmarshaller.java:137)
at com.thoughtworks.xstream.core.AbstractTreeMarshallingStrategy.unmarshal(AbstractTreeMarshallingStrategy.java:33)
at com.thoughtworks.xstream.XStream.unmarshal(XStream.java:926)
at hudson.util.XStream2.unmarshal(XStream2.java:91)
at com.thoughtworks.xstream.XStream.unmarshal(XStream.java:912)
at com.thoughtworks.xstream.XStream.fromXML(XStream.java:864)
at hudson.XmlFile.read(XmlFile.java:133)
... 10 more
Caused by: java.lang.NullPointerException
at com.michelin.cio.hudson.plugins.maskpasswords.MaskPasswordsConfig.getGlobalVarPasswordPairs(MaskPasswordsConfig.java:140)
at com.michelin.cio.hudson.plugins.maskpasswords.MaskPasswordsBuildWrapper.<init>(MaskPasswordsBuildWrapper.java:77)
at com.michelin.cio.hudson.plugins.maskpasswords.MaskPasswordsBuildWrapper$ConverterImpl.unmarshal(MaskPasswordsBuildWrapper.java:336)
at hudson.util.XStream2$AssociatedConverterImpl.unmarshal(XStream2.java:293)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convert(TreeUnmarshaller.java:82)
... 34 more
27/10/2011 1:39:51 PM jenkins.model.Jenkins$6 onTaskFailed

The jobs that failed to load were the ones that had specified passwords.

I tried to add a new password to the global Jenkins configuration, but the change did not save after I hit submit.
Reverting to 2.6.1 "fixes" the problem.