When upgrading from version 4.5.3 or older to 4.6.1 build 6 (refer to Upgrade Guide), you may have Error 500 right after completing "Remove Files No Longer Used" step. This issue happens when old cache files still call functions in removed files.
Solution
- You will need to access FTP to server
- Remove folder /PF.Base/file/cache.
New cache files will be built again automatically.