During recent work with Alfresco Share, I encountered issue similar to one described in this topic http://forums.alfresco.com/en/viewtopic.php?f=9&t=14380
Apparently this was related to swf tools generating flash preview using parameter, supplied by Alfresco. My hack was to modify following config file /home/apache-tomcat-5.5.27/webapps/alfresco/WEB-INF/classes/alfresco/thumbnail-service-context.xml
to change default flash version from 9 to 10, since more and more clients upgrade to recent version, so this becomes more actual.
After change it should look like:
<!-- Web Preview thumbnail options -->
<property name="name" value="webpreview" />
<property name="mimetype" value="application/x-shockwave-flash"/>
<property name="flashVersion" value="10"/>
Perhaps there should be more flexible way to detect version of Flash player and communicate it back to Alfresco/SWF tools to render proper code.