"MySQL server has gone away" error in Open Outreach

I've done a clean installation of Open Outreach RC9 and installed most of the APPS including event and red hen. All worked fine and I can add content etc.

I wanted to try adding new fields to exiting content types and also creating a new content type with custom fields. Initially I noticed that this wasn't possible as the field_ui module isn't installed by default. So I enabled this and got the add fields user interface ok. But as soon as I try to add a field to a content type then I get the following errors and also the site is then un-usable:

PDOException: SQLSTATE[HY000]: General error: 2006 MySQL server has gone away: SELECT COUNT(cid) FROM {comment} WHERE status = :status; Array ( [:status] => 0 ) in comment_count_unpublished() (line 314 of /Library/WebServer/Documents/openoutreach/modules/comment/comment.module).

Uncaught exception thrown in session handler.
PDOException: SQLSTATE[HY000]: General error: 2006 MySQL server has gone away in _drupal_session_write() (line 209 of /Library/WebServer/Documents/openoutreach/includes/session.inc).

Fatal error: Uncaught exception 'PDOException' with message 'SQLSTATE[HY000]: General error: 2006 MySQL server has gone away' in /Library/WebServer/Documents/openoutreach/includes/database/database.inc:2139 Stack trace: #0 /Library/WebServer/Documents/openoutreach/includes/database/database.inc(2139): PDOStatement->execute(Array) #1 /Library/WebServer/Documents/openoutreach/includes/database/database.inc(664): DatabaseStatementBase->execute(Array, Array) #2 /Library/WebServer/Documents/openoutreach/includes/database/database.inc(2318): DatabaseConnection->query('SELECT expire, ...', Array, Array) #3 /Library/WebServer/Documents/openoutreach/includes/lock.inc(167): db_query('SELECT expire, ...', Array) #4 /Library/WebServer/Documents/openoutreach/includes/lock.inc(146): lock_may_be_available('schema:runtime:...') #5 /Library/WebServer/Documents/openoutreach/includes/bootstrap.inc(420): lock_acquire('schema:runtime:...') #6 /Library/WebServer/Documents/openoutreach/includes/bootstrap.inc(442): DrupalCacheArray->set(Array) #7 [internal function]: D in /Library/WebServer/Documents/openoutreach/includes/database/database.inc on line 2139