Symptoms
The following error message is shown instead of your usual Magento page:
There has been an error processing your request
Exception printing is disabled by default for security reasons.
Error log record number: 1286489434787

Cause
Usually, it is caused by calling incompatible classes in themes, extensions or templates, database connectivity issues or resource shortage (i.e. insufficient diskspace or PHP memory_limit option).

Symptoms
Blank page is shown in Magento Frontend, Backend or Magento Connect Manager

Cause
If you see a blank page opening your Store in browser, it indicates that there is a PHP syntax error somewhere in the code of your site.
This usually happens when you modified files, templates or extensions manually, or installed a theme or extension with PHP syntax errors.

Troubleshooting
Before starting investigation please try to Disable Magento Compiler and Clear cached Magento data , in the most cases it should solve the issue.
To see the actual error message you need to login via FTP to your Store and use the following instructions:

Sometimes you may need to make sure that the user is browsing your site over securte connection. An easy to way to always redirect the user to secure connection (https://) can be accomplished with a .htaccess file containing the following lines:

After upgrading to Magento 1.6, You may face some problems like Integrity constraint violation: 1062 Duplicate entry or Error 404 after installation(while home page is OK).

It is also highly encouraged to restrict access to your website while repairing the database or making upgrade. Here is an example of restricting your website instance to your IP address exclusively. Other visitors, including search spiders, will get the HTTP 503 Service Unavailable error.

If you have experienced this error in your webpage:

Fatal error: Cannot use object of type stdClass as array in /modules/mod_jf_twitter/helper.php on line 38

Then it is a problem of “JF Twitter” module. Do the following on /modules/mod_jf_twitter/helper.php/helper.php on line 38:

My contact forms no longer work in Chrome or Safari. The form will load but errors occur upon clicking “send”. Works still in firefox and Explorer.