Have installed Free version of QuikCart 3.4 and 3.5 with the same problem. Installation goes well, adding products goes well. Adding to cart and checking out goes well. Then, the next day suddenly this happens: Adding to basket returns a blank page or a page with this: 
When hitting the browsers back button I go back to the previous page and when clicking on "Basket", I see that the product has been added to the basket. But when I try to continue to check out and go to the page where I fill out name and adress, the blank page appears again.
When clicking on the Add to Cart WORKS, the returning URL ends like this: /index.php?cesta,18
When clicking on the Add to Cart results in a blank page, the returning URL ends like this: /?cesta,18&iProductAdd=8&iQuantity=1
The funny thing is that it worked perfectly yesterday, and today suddenly the blank page appears.
perhaps the problem is how the server is set up, we had this problem here before. I helped owner of the shop to solve it by rewriting parts of the script. Your web server may not be configured to accept requests with simple ?, like for example: http://www.yourserver.com/?search-results,19&sPhrase=ddd
Try that URL, works? if not, it's your server.
There is more here: http://opensolution.org/Quick.Cart/forum/?p=readTopic&nr=6328
I have installed and reinstalled all day. Testing after every little change. ANd sooner or later the blank page is there and I start over again. This afternoon the first "blank" page (same issue, add to basket) appeared after changing "Producers" and "Categories" in config/lang_en.php
Strange thing is that Quick Cart has been working perfectly for several weeks. All fine tuning of translation, change of header picture, change of the words Producers and Categories, installing Send to Client email plugin, change to pointspace stylesheet etc was done. Before adding about 120 products, we made sure everything was running OK. Then we finished adding products yesterday, and as soon as we opened up for the general public the blank page problem started.
Just transfered back via ftp the original config/lang_en.php. Works OK again. Then I again changed producers and categories and this time it is still working. I did nothing diferrent this time. I will have to continue tomorrow.....because this "on" and "off" is strange.
I had similar problem with every verison of QCMS and QCart and it occurs if I use Dreamweaver to edit the files in config library. I just tested to change "Producer" in config/lang_en.php and after that logged in and clicked on "Save" in admin/settings. If I then log out and go back to the site a white page with the text: $config['title'] = "QuickCart - fast and simple shopping cart"; is just what is left. Checking the file config/lang_en.php shows that the file is completely empty except for this line: $config['title'] = "QuickCart - fast and simple shopping cart"; The funny thing is that everything will be OK until I click on "Save" in admin/settings. It is then the content of the file config/lang_en.php will be erased except for the line mentioned above.
If I do not use Dreamweaver as editor this problem will not occur.
sorry beholder, I was getting so tired of all this last night so I simply clicked on your link when I read your post. But yes, the url works. And remember, quick cart has been working perfectly for several weeks while we have been adding products.
cgan...at the beginning, when we first installed quick cart, I think we had something similar to what you explain as well. However, editing is made in notepad and uploading we do with either FTP Commmander or Cute FTP.
This morning quick cart is still working after last nights final reinstall. But this afternoon we will switch to the pointstyle stylesheet and also add the plugin SendEmailToclient. I am crossing my fingers...
We are using the free version because at the moment we do not need more functionality.....but if we switched to a paid version (I dont mind buying it) would quick cart be more stable with regards to this issue?
I'd recommend to stick to the free version for a few weeks if you're having this kind of problems. Do you still have the non-working version somewhere at FTP? we could try to investigate..
beholder.......the QC 3.5 whith the issue of "Adding to basket returns a blank page" has been working fine for 10 days now. Only thing we have not been able to restore is the SendEmailToClient plugin.
When we do add this, the blank page thingy comes back. Then we restore the files that were modified for the plugin, and we are back to normal working functionality.
this must be checked for sure. I am willing to install that plugin for you (directly via FTP to your shop) and hopefully I will find out would what's wrong with your setup/server. If possible, send login credentials to my address displayed at this page: http://www.tigerware.sk/easyplugins/
