VS 2010 Save To File?

I need a better solution that what I am currently using, and not sure where to go from here.The program uses a scanner and scans documents into it. It uses a flat file (essentially a csv) to store data captured from the documents being scanned (each line in the file is one "document", with each value in the line being some piece of data from that document).

The scanner can scan up to 100 documents per minute, so it runs very fast.Currently, when a document is scanned in, the flat file is opened, a line written to it, then closed.It works for the most part, but sometimes i guess it's too fast for the IO operation, and some documents get completely missed. It will throw an error "error accessing file....". I assume this is because the file is still open from writing the last document to it.

Documents can be scanned at random, so they aren't always constantly scanning. It may scan 100 at a time now, then wait 10 minutes, and then scan one document.Database is not an option, per the specs of this program. It must be flat files. If theres a way to use a flat file like a database, that's cool. It doesn't have to be in CSV format.

It MUST be able to write to the file immediately after scanning. I worry about leaving the file open for writing constantly while the program is open because of a system failure or crash, the file may get corrupt or lost. That is not acceptable. It must be the best option for data recovery, should the computer crash or power go out, etc.