I would list more information about your system specs, including sound card in use, GPU, CPU, memory type, system motherboard. “Speccy” is a good tool for this, and can export to a text format. Then post the summary section into the post.
List your version and build number of Windows and Vegas.
Make sure your Windows is up to date, and drivers up to date. Also make sure to include .net updates in windows update.
If you know how, run memtes86+ (https://www.memtest.org/) and verify your memory has Zero errors across multiple runs.
Run SFC /SCANNOW from an admin command prompt. This verifies the integrity of your windows core files. You should get a “Windows Resource Protection did not find any integrity violations.” response.
Check your system DPC latency with:
https://www.thesycon.de/eng/latency_check.shtml or https://www.resplendence.com/latencymon
List your source media format (using “media info” app.) List your intended workflow from source, to timeline ,to export format.
The last time I had this File IO error was way back, and my issue was with a really old high end Sound Blaster card. Once I removed it and the drivers, then switched to the newer on-board card the problem went away. That is why I suspect something with your configuration or workflow.
The community is really good at helping people that list enough details about the problems they are having.
Most of us did not put enough points into Divination, to read minds from a far.