The problem may be caused by the fact that the proxy server currently selected in A4Proxy “as default” is not working. A4Proxy offers you a lot of proxies and you can pick any one of them by right-clicking on it and selecting “Set As Default” on the context menu that will appear. The option “Use a new proxy on each request” (Proxy Options tab) and other proxy rotation options must be disabled for this to work.
You must check all proxies, sort them by speed (click on the Response Time column header on the Proxy Check tab, so that the proxies with the least response time number (i.e. the faster ones) will be at the top). Then select one of the proxies with a green circle on the left, as described above. If you have difficulty with a particular proxy, select a different one and see if it makes any difference.
If you want to change proxies automatically for each request, you must check the database from time to time and make sure that all good proxies are grouped at the top of the list and the appropriate number of proxies to use is entered in the option “Use {x} proxies from {0} position”.
Another possible explanation is that the access to the page may indeed be blocked by the particular proxy. Some proxies block access to certain pages. A4Proxy cannot detect such proxies automatically but you can do it manually, more or less easily. Here’s how to do it.
Enter the URL of a page which gets blocked in such proxies into the input field on the Proxy Check tab (intended for URL checking). Highlight (select) some proxies and press the Check URL button. A4Proxy will load the page through all proxies you selected and show some statistics in the proxy table (you will need to scroll the table to the right in order to see the last three columns – ‘URL Respose Time’, ‘Bytes Received’ and ‘Speed’).
After the page has been successfully downloaded, in theory the contents of the ‘Bytes Received’ column must be identical for all the proxies, because it is one and the same page and it should have the same size no matter which proxy you use to load it. BUT, if a particular proxy blocks access to that page, you will get a message saying that the page is blocked, instead of the page itself. And the SIZE of that message (in bytes) will certainly be different from the size of the normal page. Now you can simply sort the proxies by the Bytes Received column and disable or remove those which show “wrong” figures. E.g., 8 out of 10 proxies show the size of the page as 19083 bytes, one shows 1298 bytes and one – 13657; clearly these two proxies show their own messages instead of the original page.
Note that you may have a similar error message when trying to access a secure website (i.e. one which uses HTTPS protocol) via a proxy which doesn’t support that protocol. Look at the proxy list (Proxy Check tab), scroll the table to the right to see the HTTPS column. ‘X’ in this column indicates that the proxy supports Secure HTTP protocol. Make sure that the proxy selected as default has an X in this column.
In order to test proxies for HTTPS support, you should enable the option “Check for FTP/HTTPS support on reset data” (Proxy Options tab) and enable the “Reset Data” option on the Proxy Check tab before checking proxies.