Which version of C5 and PHP do you use?
Is it possible to reproduce the error in a xampp/lampp or mampp sandbox?

If it is reproducable, could you pastie the part of your customization that you think is producing the error?

I usually comment out everything unimportant and comment things out line by line, to make the code understandable again.
Yes I know, debugging is easier, but behaviours..

I'm using 5.3.3.1 and I'm already local on my machine using mamp.

here is lines of code from that file that is throwing the errors on.

if (is_object($bf) && (!$bf->isError()) && $bf->getFileID() > 0) {
$fileID = $bf->getFileID();
$selectedDisplay = 'block';
$resetDisplay = 'none';
}

$html = '<div id="' . $id . '-fm-selected" class="ccm-file-selected-wrapper" style="display: ' . $selectedDisplay . '"><img src="' . ASSETS_URL_IMAGES . '/throbber_white_16.gif" /></div>';

$html .= '<div class="ccm-file-manager-select" id="' . $id . '-fm-display" ccm-file-manager-field="' . $id . '" style="display: ' . $resetDisplay . '">';
$html .= '<a href="javascript:void(0)" class="ccm-file-manager-launch" onclick="ccm_chooseAsset=false">' . $chooseText . '</a>';
if ($filterArgs != false) {
foreach($filterArgs as $key => $value) {
$html .= '<input type="hidden" class="ccm-file-manager-filter" name="' . $key . '" value="' . $value . '" />';
}
}
$html .= '</div><input id="' . $id . '-fm-value" type="hidden" name="' . $postname . '" value="' . $fileID . '" />';

weird error... all i did was re-download the zoom-image package...over write the old zoom_image file and it works. sorry for the confusion.

nice to hear you fixed it ;)
where's that site, is it online yet?

For all who encounter the same problems:
It is probably a permission issue.
chmod or chown the files correctly.
Make sure a file is not exclusively locked, in example by your editor.
clear the cache.

old version I think..

There was a change in the c5 api which broke the zoom image block