I have been experimenting with the REST API recently. My work cycle involves running my test program which add nodes a relationships to my graphDB, then deleting them by using neo4j-shell with a Cypher command as preparation for the next test run. All was well until the deletions started failing. At first I thought this was because my deletions encompassed too many nodes for a single transaction, so I tried to restrict the scope. It doesn't help. I'm seeing this...

```
neo4j-sh (?)$ match (s:Tweeter)-[m:Tweet]->(r:Tweeter) where s.handle =~ '@C.*' delete s,m,r;
+-------------------+
| No data returned. |
+-------------------+
Nodes deleted: 12
Relationships deleted: 21
80 ms
TransactionFailureException: Transaction was marked as successful, but unable to commit transaction so rolled back.

```

I don't know what to try next. I see no clues in the server log.