File uploads simply do not work - what could be wrong server side?

This has been grinding my gears for at least a week now.

I have a site which has a crucial function - the upload component. Without it, the site is completely useless.

Now, lots of users have problems uploading files. This is why I implemented a log system that keeps track of what happens when the file is on the server.

Problem is, only a minority of problems happen when the file is on the server, the problems happen client side.

For example, when I tried SWFUpload the errors where 'I/O Error'. When I changed to Uploadify I get 'HTTP Error'. I am trying to get a more detailed error description as I type this.

I am starting to think its not the client or the upload software, but the server. What could be wrong? The following directives for PHP are set:

upload_max_filesize 200M
post_max_size 200M
memory_limit 256M
max_execution_time 4200
max_inpu开发者_高级运维t_time 4200

I simply have no clue why file uploads are failing. They should not fail. I would really appreciate any answers as why the uploads could be failing.

Thank you.

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Are you using enctype="multipart/form-data" as an attribute in your HTML form element?