See thread here for more on this problem. I was able to find a solution for my system:
forum.joomlaworks.net/index.php?topic=569.msg2297#msg2297

I'm running a local intranet for me and my neighbors, and I have the same problem but I don't know exactly where I need to check my "permissions".  I've looked at the showthumb.php file itself, but I don't see anything related to permissions.  Anything thoughts? ???

no, you won't see anything about permissions IN the file. You need to use CHMOD (in your FTP) to change the permissions associated with the module files and directory on the server/your mambo/joomla installation.

CHMOD:
en.wikipedia.org/wiki/Chmod

If you are setting up some kind of intranet, especially wifi, you better study up on permissions and other security issues!

See, I don't have to FTP anything... It's all on my "local" machine.. and as far as the securities go, they are well aware of big brother.. LOL..

Well you must be running off your own server then, a pc set up as a server maybe, with some kind of *nix system? CHMOD is a unix/linux/etc command. You still have file permissions you need to work with.

I'm having trouble with thumbs not showing up, too. I've implemented all the fixes that the minked frappe  :P drinker suggests:

• my permissions are set as suggested
• my XML declaration is killed
• I've disabled all the javascript on my site except that related to SIG--and the script used by GoDaddy.com to display Google Ads at the top of the screen on all their free, ad-supported hosting sites (like mine).

I can't turn the GoogleAd script off without actually (gasp!) paying for my hosting service! :o

Does anyone else out there use GoDaddy? Any luck with SIG? Would love to know!

--Luke

Well you must be running off your own server then, a pc set up as a server maybe, with some kind of *nix system? CHMOD is a unix/linux/etc command. You still have file permissions you need to work with.

Yes, my system is the server.. Actually XP Pro running wamp/apache/sql, etc..  Anyways, if there is a permission issue, then where do I resolve this? ???  Also what is the GD Image Library?

this stuff is basic. use google to look up CHMOD and GD Image Library. software support forums are not a good place for step-by-step instructions on fundamentals. the information is widely available already.

Alright guys,

Well I was having exactly the same issue and then noticed that all the jpg's that were not showing as thumbnails were not named in the standard way eg. had spaces, + etc in the title.

So I renamed a file to have say joe_blogg instead of joe+blogg and the thumbnail magically appeared!!!!

Hope this helps, not a perms issue

Nils

Hi;

I have the same problem and i have done everything, but it still doesnt work.

Guys, i think, it is nor about CHMOD etc. Because my thumbs were working fine. Then someday they began not to work. What is changed?

Only thing, which is changed during that time, is the UPDATES of BROWSERS.

Guys, The problem is not about CHMOD etc, it is about BROWSER UPDATES. (firefox and  IE)

I think, the turn is SIG teams.