Error on rename of './civicrm_dev/civicrm_pcp_block' to './civicrm_dev/#sql2-2534-3a7d4' (errno: 152) during upgrade to 4.1.alpha1

During the database upgrade from 4.0.8 to 4.1.beta2 i get an error:
PEAR_Exception: DB Error: unknown error in CRM_Core_Error::exceptionHandler() (line 533 of /home/www/sites/dev/sites/all/modules/civicrm/CRM/Core/Error.php).

In http://svn.civicrm.org/civicrm/branches/v4.1/CRM/Upgrade/Incremental/sql/4.1.alpha1.mysql.tpl all changes until CRM-8534 have been made to the database.

The following section has not yet been made:

– CRM-8534
ALTER TABLE civicrm_pcp_block
DROP FOREIGN KEY FK_civicrm_pcp_block_entity_id,
DROP INDEX FK_civicrm_pcp_block_entity_id;

Trying to apply this change manually I get the following SQL error:
Error
SQL query:
ALTER TABLE civicrm_pcp_block DROP FOREIGN KEY FK_civicrm_pcp_block_entity_id,
DROP INDEX FK_civicrm_pcp_block_entity_id

MySQL said:
#1025 - Error on rename of './civicrm_dev/civicrm_pcp_block' to './civicrm_dev/#sql2-2534-3a7d4' (errno: 152)

The table is the following:

–
-- Table structure for table `civicrm_pcp_block`
–

CREATE TABLE IF NOT EXISTS `civicrm_pcp_block` (
`id` int(10) unsigned NOT NULL auto_increment COMMENT 'PCP block Id',
`entity_table` varchar(64) collate utf8_unicode_ci default NULL,
`entity_id` int(10) unsigned NOT NULL COMMENT 'FK to civicrm_contribution_page.id',
`supporter_profile_id` int(10) unsigned default NULL COMMENT 'FK to civicrm_uf_group.id. Does Personal Campaign Page require manual activation by administrator? (is inactive by default after setup)?',
`is_approval_needed` tinyint(4) default NULL COMMENT 'Does Personal Campaign Page require manual activation by administrator? (is inactive by default after setup)?',
`is_tellfriend_enabled` tinyint(4) default NULL COMMENT 'Does Personal Campaign Page allow using tell a friend?',
`tellfriend_limit` int(10) unsigned default NULL COMMENT 'Maximum recipient fields allowed in tell a friend',
`link_text` varchar(255) collate utf8_unicode_ci default NULL COMMENT 'Link text for PCP.',
`is_active` tinyint(4) default '1' COMMENT 'Is Personal Campaign Page Block enabled/active?',
`notify_email` varchar(255) collate utf8_unicode_ci default NULL COMMENT 'If set, notification is automatically emailed to this email-address on create/update Personal Campaign Page',
PRIMARY KEY (`id`),
KEY `FK_civicrm_pcp_block_entity_id` (`entity_id`),
KEY `FK_civicrm_pcp_block_supporter_profile_id` (`supporter_profile_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci AUTO_INCREMENT=1 ;