Sugar 4.5.1e: E-Mail attachments not shown

[markers1]

I am unable to view any attachments to e-mails.
I am running Sugar OpenSource v4.5.1e on a Fedora Core 6 system:
PHP 5.1.6
Apache 2.2.4
MySQL server 5.0.27

Client browser: Firefox 2.0.0.3

Steps to reproduce:
Choose an opportunity
In the history subpanel, click on an archived E-mail which has a (separately uploaded) attached document.
The E-Mail details are then shown with a list of attachments below the body section. (sugarcrm.log shows: modules/Emails/DetailView.php )
Click on the link for one of the attachments and the browser then shows an empty page. No attachment to be seen anywhere.

Expected results:
Click on the link for one of the attachments and the browser then prompts to download the attachment file.

When clicking on the attachment link, no new lines appear in either the apache error_log or access_log or in the sugarcrm.log files.

Many thanks in advance for any hints as to where else I should look for the cause of this problem.

[markers1]

Further investigation showed that the caching of the browser was complicating things - this was one reason why there were no new entries in the error_log or access_log files.

After restarting the browser, I found the following message in the apache error_log file:

[Tue Sep 04 09:58:51 2007] [error] [client 192.168.1.120] PHP Fatal error:  Call to undefined function mb_encode_mimeheader() in /var/www/html/crm/download.php on line 69, referer: http://192.168.1.91/crm/index.php?module=Emails&action=DetailView&record=c4004a00-d730-cf81-5a52-46d580b29a56

This provided the hint that I needed.

The solution was then to install the php-mbstring RPM.

Attachments are now being shown. Problem solved.