Faced this issue today with 1.2.9...
For those, who unfamilliar with bugtracking system...
File: /var/www/imscp/engine/PerlLib/Modules/Subdomain.pm
Line 248 find : SHARED_MOUNT_POINTS => $self->_sharedMountPoint(),
Change to: SHARED_MOUNT_POINT => $self->_sharedMountPoint(),
Then go to admin/imscp_debugger.php and click last queue to re-run it.
Hope fix will be included in future releases.