VirtualBox 4.0.4 does not recognise Solaris.vdi it just created on MacOS 10.6

[Richard A. O'Keefe]

0. Use Mac OS X 10.6.6 on a 2.66 GHz Intel Core 2 Duo iMac 9.1.
1. Download and install VirtualBox 4.0.4.
2. Create a new virtual machine to run Solaris.
3. Install OpenSolaris.
4. Within OpenSolaris, install about 150 packages.
5. Go home for the weekend.
6. Come back to find the Solaris window greyed and press Host-P to wake it up,
7. Failed to open a session for the virtual machine Solaris.

   Could not open the medium '/home/...VirtualBox/HardDisks/Solaris.vdi'.
   VDI: invalid pre-header in ... same file name ... (VERR_VD_VDI_INVALID_HEADER).
   VD: error VD_VDI_INVALID_HEADER opening image file ... same file name ... (VERR_VD_VDI_INVALID_HEADER)
       Result Code: NS_ERROR_FAILURE (0x80004005)
       Component: Medium
       Interface: IMedium {9edda847-1279-4v0a-9af7-9d66251ccc18}
   

8. Discover that file does exist and is readable and writable.

   m% ls -l /home/...VirtualBox/HardDisks/Solaris.vdi
   -rw-------  1 ok  csstaff  9700446208 28 Feb 10:41 /home/...VirtualBox/HardDisks/Solaris.vdi
   m% wc /home/...VirtualBox/HardDisks/Solaris.vdi
   71471861 389330678 9700446208 /home/...VirtualBox/HardDisks/Solaris.vdi
   

This problem has not arisen on a MacBook Pro running 10.5. Two possibly relevant differences are that the laptop is mostly 32 bit while the desktop machine is mostly 64 bit, and that the laptop files are local (Mac filesystem) but the desktop files are served over NFS (mount says "map auto_home on /home (autofs, automounted, nobrowse)")