When resolving an issue I get an error mail

When the issue will be resolved, the project leader gets a validation email. The email header is correct (e.g. [JIRA] Resolved (XX-1) "description" ) But in the email there ist a long error message:

An error occured whilst redering this message. Please contact the administrators, and inform them of this bug.
Details:
______
org.apache.velocity.exception.MethodInvocationException: Inovation of method 'printChangelog' in class
com.atlassian.jira.util.JiraVelocityHelper threw exception class
com.atlassian.jira.issue.customfields.impl.FieldValidationException : Invalid status name "Open".
at
org.apache ....

The status settings for the issues are right, only the emails when its closed make problems.
Is there maybe a problem with the SMTP server or did I make a wrong setting in the workflow or notification scheme?

Thanks, Fabian