Found in 2.0.7 - here is the stack trace:
java.lang.NullPointerException at
org.visres.merge.MergeContacts.setFirstContactDates(MergeContacts.java:241)
at
org.visres.merge.MergeContacts.merge(MergeContacts.java:96)
at
org.visres.merge.MergeContacts.merge(MergeContacts.java:51)
at
org.visres.merge.servlet.Worker.merge(Worker.java:116)
at
org.visres.merge.servlet.MergeServlet.handlePost(MergeServlet.java:128)
...
Logged In: YES
user_id=34516
Fixed in 2.0.8