Troubleshooting a Failed Opening Required file Error
When accessing parts of WHMCS, the following Oops error may be encountered:
main(): Failed opening required '/path/to/whmcs/..filename.php'...
A required file is missing.
In this example, the /whmcs/includes/orderfunctions.php file was deleted.
Upload the missing file to the folder path specified in the error message.
We recommend a fresh re-upload of all the WHMCS files to ensure that no other files are missing.
The Full Release files can be downloaded from https://download.whmcs.com
Please ensure all files are overwritten successfully.