I have been at this for a week and am VERY frustrated by this problem:
Unknown Archive type
Gallery upload error. Cannot extract archive.
A little background: I started developing the site on my local machine using WAMP, with Apache 2.2.2 and PHP 5.4.3
Joomla is 2.5.11
K2 is 2.6.7
I want to see how all of this works together so rather than buy SIGPRO for something that may not work for my needs, I used SIG Free and with a couple of hacks to some K2 files, I have it working, sort of, and that is where I am now. I have Googled this forum for every instance of this issue (and there are WAY too many for this to be just user issues) and I have searched the net for many possible variations of this error. Most lead back here.
The majority of the solution here have been that this is a path error and I simply do not believe that to be the case! Here is why:
I have the same Joomla/K2 configuration running on 2 free host sites as well as my local host, to try to figure this out
The common thread thru all of them is that I can create the items with image galleries on all 3 installs WITH IE8!
On 1 host I can save the galleries correctly and perfectly with BOT IE8 and Firefox 22
on the other host, Firefox fails every time with the above error while IE8 is perfect!
On LOCALHOST, again IE8 is perfect and Firefox fails!
The path in SIG plugin in all 3 instances is MEDIA/K2/GALLERIES
The paths in Joomla Media Manager is FILES folder=MEDIA/K2 and IMAGES folder= MEDIA/K2/GALLERIES
So the conclusion is that this is NOT a path problem because IE8 works perfectly on all three installs and FIREFOX FAILS ON THE SAME SETUP ON THE SAME ITEMS on 2 of 3!
Where it gets odd is that on one host, BOTH IE8 and Firefox work perfectly!
SO this HAS to be something in the PHP settings that JOOMLA chokes on!
On one host, where everything works perfectly, I can see the PHPINFO in Joomla back end, but the other has it blocked (security reasons). I compared my localhost settings to the perfect host but cannot see any differences.
Since I have SIG Free working perfectly in this installation with IE8 AND Firefox on one host, it is NOT a compatibility problem with not having SIGPRO and K2 and since the BULK of the discussion on this very issue on the forum ALL have to do with SIGPRO, the issue is not with it either!

I am hoping someone with a little more PHP and Joomla experience can shed some light on this. My suspicion is that the gallery folder id number that is used to create the folder in the gallery path is some how being corrupted thru a PHP conflict. I HAVE turned on errors in Joomla up to the development level and this does not pop any errors, nor are there any errors in the server logs that point to anything that I can see.

Hello grh,

For issues regarding SIGPRO you can use the JoomlaWorks ticketing system or the the contact form for presales questions.

For free extensions and any issues related with them please use the community forum.

Please read the entire post. The issue is with SIG Free not SIG Pro. And mostly it has to do with K2 and PHP with Firefox and IE8. I KNOW where to find assistance with SIGPRO but that is not what I requested.

I would appreciate anyone with experience and knowledge of those two issues assisting in working out the problem.