Said this on the Fual thread.. should post here too..
The exact answer appears to be that the issue with IH2 & additional images is a webhost specific issue based on how php is implemented on some hosts. Like I posted earlier, if you look through this support thread (posts from the last 3-4 days) the details are fully explained.. (You SHOULD take the time to read through)
I think however is that part of the issue is that you did not properly merge the includes/modules/your template/additional images.php files that come with both Fual Slimbox and IH2. Merging the two should resolve any conflicts. This is not an easy job since Fual was written for Zen 1.3.8 and the Fual specific changes are not super obvious. It will take doing some comparisons between the Fual files and Zen 1.3.8 to make note all of the Fual modifications. Then compare that to the latest Zen Cart version to merge in any current Zen version specific changes. Then FINALLY comparing the file to the Image Handler version and incorporating the IH2 specific modifications.
FYI, the current version of Fual may have issues on PHP 5.3 servers as it appears to still contains functions I believe are deprecated in PHP 5.3. (Still need to confirm this when I get around to trying to convert Fual for Zen 1.3.9 for my test store..)
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