Please try upgrading your site to the latest version of Showkase v1.7.6.
There was a fix in v1.7.1:
Fixed uploader shows green success icon after an error.
Even if the upload still fails, at least we should now get a description of the error which should hopefully point us in the right direction.
The upload module itself was updated in v1.7.4:
Updated to latest versions of PHPMailer, Smarty, CKEditor, jQuery UI, Plupload and jsTree
Also, after you have installed v1.7.6, please apply the patch I created as I fixed a couple of upload module problems (caused by PHP 8.1 and PHP 8.2 deprecations) and updated the upload module once again.
You can find instructions to upgrade Showkase here.
I've reactivated your download link and you should receive an email containing the link so that you can download the latest version of Showkase v1.7.6.
The patch I created can be found in this forum post.
More information about applying the patch can be found here.
Hopefully, updating your site to Showkase v1.7.6 + patch will resolve your problem without any further action.
However, if you continue to experience difficulties, please let me know and I'll try to help further.
Thank you.
Note:
Please be sure to make a complete backup of your existing site before upgrading. You should not experience any problems during the upgrade process but it would be wise to have a backup in case anything goes wrong and you need to reinstate your original files at a later date.