The MAX_FILE_SIZE item cannot specify a file size greater than the file size that has been set in the upload_max_filesize ini-setting. The default is 2 Megabytes.
If max_execution_time is set too small, script execution may be exceeded by the value. Make sure you set max_execution_time large enough.
Note: max_execution_time only affects the execution time of the script itself. Any time spent on activity that happens outside the execution of the script such as system calls using system(), the sleep() function, database queries, time taken by the file upload process, etc. is not included when determining the maximum time that the script has been running.
max_input_time sets the maximum time, in seconds, the script is allowed to receive input; this includes file uploads. For large or multiple files, or users on slower connections, the default of 60 seconds may be exceeded.
If post_max_size is set too small, large files cannot be uploaded. Make sure you set post_max_size large enough.
Not validating which file you operate on may mean that users can access sensitive information in other directories.
Please note that the CERN httpd seems to strip off everything starting at the first whitespace in the content-type mime header it gets from the client. As long as this is the case, CERN httpd will not support the file upload feature.
Due to the large amount of directory listing styles we cannot guarantee that files with exotic names (like containing spaces) are handled properly.
A developer may not mix normal input fields and file upload fields in the same form variable (by using an input name like foo).