[imp] Weird problem with certain attachments

[imp-archive@cloud9.net]

I'm using Horde 3.0.10 and IMP 4.0.4 with Apache 2.2.0, PHP 5.1.2, and 
ZendPlatform 2.1.2 and I have started to observe the following issue:

I send an e-mail with one 1MB Windows bitmap from Outlook 2003 and I'm 
able to view it fine using IMP.

An e-mail with two or more bitmaps and I get a blank page.  I get the 
following error at when I turn on all PHP messages to the browser:

Fatal error: Call to a member function loadString() on a non-object in /webmail/horde/imp/lib/MIME/Viewer/images.php on line 228

My php.ini:

session.use_cookies = 1
file_uploads = on
upload_max_filesize = 15360000
register_globals = on
error_reporting = E_ALL & ~E_NOTICE
upload_tmp_dir = /tmp
safe_mode = off
include_path = /lib/php
memory_limit = 16M
max_execution_time = 180
post_max_size = 15360000

[Zend]
zend_extension=/Zend/lib/ZendExtensionManager.so
zend_extension_manager.platform=/Zend/lib/Platform-2.1.2
zend_extension_manager.optimizer=/Zend/lib/Optimizer-2.6.2
zend_extension_manager.download_server=/Zend/lib/DownloadServer-1.0.6
zend_extension_manager.mysql=/Zend/lib/MySQL
zend_extension_manager.gd=/Zend/lib/GD
zend_extension_manager.debug_server=/Zend/lib/Debugger-5.1.0
;zend_extension_manager.mod_cluster=/Zend/lib/SC-1.0.2
zend_ini_file=/Zend/etc/zend.ini
zend_platform.version=2.1.2

Are there any other places I should look for the origin of this issue?  I 
am also building a 3.1.x/4.1.x setup for testing but it is not ready to go 
into production yet.

--
Mark P. Hennessy