When developing Magento modules this is one of the common errors you will encounter.
The error is caused by these 3 most common mistakes:
1. When creating a new module you always have to create a helper file, even though you are not using it. This is just how Magento works. If you want to know how to create a helper file in module, go to this blog post.
2. The second most common mistake is the wrong structure in the XML config file.
Magento strictly follows a structure in XML files, having something wrong or having a typo somewhere always leads to an error. The correct structure for defining new helper in etc/config.xml is as follows:
<global> <helpers> <unique_identifier> <class>Package_ModuleName_Helper</class> </guides_meta> </helpers> </global>
Make sure that your helper definition follows the above structure.
3. If you are sure that everything from above is correct but you still get the same error then there is one more thing. Turn of the code compilation.
You can do it from Administration by going to System > Tools > Compilation > Disable compilation.
Or if for some reason don’t have access to Admin are, you can execute these shell commands.
php -f shell/compiler.php -- disable php -f shell/compiler.php -- clear php -f shell/compiler.php -- state