I have read several posts in this forum, none of witch confirm a solution.

I have spent many hours on trying to solve the problem

Here it is:

When I try and upload a zip archive in K2 I get an error:

       * UNKNOWNARCHIVETYPE
       * Gallery upload error: Cannot extract archive!

I have checked all of the directories mentioned in prevoius posts and changed them to 777

I can upload and extract zip's in cpanel, extplorer and ftp without a problem.

I have contacted my host and they cannot find a problem

Please could you help

I no longer have the issue with the uploading of zip archives and all displays as it should.

I am using the latest version of the SIG plugin as of todays date.
Joomla 1.5.20
PHP, MYSQL all meet the requirements

To resolve your problem Follow this. From community.getk2.org

I had this same problem. When uploading to the gallery, the mime type is checked and it appears that it was checking the path for the mime type and not the name of the file. There are several checks for mime type prior to the code I edited below, and even some after. It keeps trying different ones until it gets a hit. Unfortunately until I fixed the code, it was trying to call it a text file and not a zip file. Anyway, this is what I did:

File: \administrator\components\com_k2\lib\class.upload.php
Line: ~2231
Change...
$this->file_src_mime = mime_content_type($this->file_src_pathname);
...to...
$this->file_src_mime = mime_content_type($this->file_src_name);

There was no need for my hosting company to get involved.
My directories are back to 755 and working fine.
I have Mootols upgrade plug in working take sit to version 1.4

If you still have issues... read this thread.

community.getk2.org/forum/topics/k2-sig-pro-gallery-upload?id=3536014%3ATopic%3A1938&page=2#comments

Hope this helps