Exception adding an image on a new post

I was writing a new blog post, and tried to add an image. The image popup window returned an exception page.

I've attached the html output to the issue (too large to paste inline)

Minimal exerpt:
Cause
org.apache.velocity.exception.MethodInvocationException: Invocation of method 'hasAttachFilePermissions' in class com.atlassian.confluence.pages.actions.InsertImageInDraftAction threw exception java.lang.IllegalStateException: Space does not exist at /users/insertimage-popup-common.vm[line 25, column 52]
at org.apache.velocity.runtime.parser.node.ASTMethod.handleInvocationException(ASTMethod.java:337) caused by: java.lang.IllegalStateException: Space does not exist
at com.atlassian.confluence.security.delegate.AttachmentPermissionsDelegate.canCreate(AttachmentPermissionsDelegate.java:88)

Stack Trace:
org.apache.velocity.exception.MethodInvocationException: Invocation of method 'hasAttachFilePermissions' in class com.atlassian.confluence.pages.actions.InsertImageInDraftAction threw exception java.lang.IllegalStateException: Space does not exist at /users/insertimage-popup-common.vm[line 25, column 52]
at org.apache.velocity.runtime.parser.node.ASTMethod.handleInvocationException(ASTMethod.java:337)