In your CE installation, there is a file_integrity.php file that resides in the root /clientexec directory. If you view that in a browser, it will show what, if any, files are corrupted or missing.
Example, checking file integrity:
If there are any problems, they will be listed as below:
File signup.php is corrupt
File install.php is missing
File templates/Raleigh/signup/signup_header.tpl is corrupt
File templates/Raleigh/signup/include/boxsubmitback.tpl is corrupt
You will notice the 'corrupt' or 'missing'. Of course the install.php should be 'missing', but others should not be 'corrupt' unless you have modified them. First action is to re-upload the files in question in binary mode.
Always check this file first, even before submitting a ticket, as this will possibly save you a great deal of time in troubleshooting and getting your billing solution back online quickly.
I checked and my site says "All files are OK", but i am missing knowledgebase
You may want to open a ticket about this.