Eclipse Content Assist

So last week, as far as I know, no changes were made to my machine, no updates were installed in eclipse and nothing was changed overall on my system, but Friday morning when I started up eclipse the content assist would show an error window and wouldn't assist me anymore with development.
The error says, "The 'org.eclipse.jdt.ui.JavaAllCompletionProposalComputer' proposal computer from the 'org.eclipse.jdt.ui' plug-in did not complete normally. The extension has thrown a runtime exception.
When I look in the .metadata/.log file I see the following stack traces:

!ENTRY org.eclipse.ui 4 0 2013-10-11 11:38:28.802
!MESSAGE Unhandled event loop exception
!STACK 0
java.lang.ClassCastException: org.eclipse.jdt.internal.core.SourceType cannot be cast to java.lang.String
at org.eclipse.jdt.internal.core.JavaModelManager.secondaryTypesSearching(JavaModelManager.java:4579)
at org.eclipse.jdt.internal.core.JavaModelManager.secondaryTypes(JavaModelManager.java:4438)
at org.eclipse.jdt.internal.core.NameLookup.findSecondaryType(NameLookup.java:591)

!ENTRY org.eclipse.jdt.ui 2 0 2013-10-11 11:38:29.270
!MESSAGE The 'org.eclipse.jdt.ui.JavaAllCompletionProposalComputer' proposal computer from the 'org.eclipse.jdt.ui' plug-in did not complete normally. The extension has thrown a runtime exception.
!STACK 0
java.lang.ClassCastException: org.eclipse.jdt.internal.core.SourceType cannot be cast to java.lang.String
at org.eclipse.jdt.internal.core.JavaModelManager.secondaryTypesSearching(JavaModelManager.java:4579)
at org.eclipse.jdt.internal.core.JavaModelManager.secondaryTypes(JavaModelManager.java:4438)
at org.eclipse.jdt.internal.core.NameLookup.findSecondaryType(NameLookup.java:591)
at org.eclipse.jdt.internal.core.NameLookup.findType(NameLookup.java:697)

!ENTRY org.eclipse.jdt.ui 4 2 2013-10-11 11:38:29.425
!MESSAGE Problems occurred when invoking code from plug-in: "org.eclipse.jdt.ui".
!STACK 0
java.lang.ClassCastException: org.eclipse.jdt.internal.core.SourceType cannot be cast to java.lang.String
at org.eclipse.jdt.internal.core.JavaModelManager.secondaryTypesSearching(JavaModelManager.java:4579)
at org.eclipse.jdt.internal.core.JavaModelManager.secondaryTypes(JavaModelManager.java:4438)

!ENTRY org.eclipse.jdt.ui 4 0 2013-10-11 11:38:29.427
!MESSAGE Error in JDT Core during AST creation
!STACK 0
java.lang.ClassCastException: org.eclipse.jdt.internal.core.SourceType cannot be cast to java.lang.String
at org.eclipse.jdt.internal.core.JavaModelManager.secondaryTypesSearching(JavaModelManager.java:4579)
at org.eclipse.jdt.internal.core.JavaModelManager.secondaryTypes(JavaModelManager.java:4438)
at org.eclipse.jdt.internal.core.NameLookup.findSecondaryType(NameLookup.java:591)
at org.eclipse.jdt.internal.core.NameLookup.findType(NameLookup.java:697)


I don't know what they mean and I can't find anything online to solve the problem. The work around I've found is to delete the following folder:
<workspace>/.metadata/.plugins/org.eclipse.jdt.core

Then the next time I start eclipse content assist works.