The process cannot access the file when posting picture

When posting a picture I get the message:

System.IO.IOException "," message ":" The process can not access the file "C: \\ Windows \\ TEMP \\ image.jpg 'because it is being used by another process.

This is only if you run it as a scenario (population) with multiple vusers.
If you do a check with 1 vusers then this goes well multiple times in a row

The picture is posted in a request as text:

Full error message:
{"versionInfo":{"hasModuleVersionChanged":false,"hasApiVersionChanged":false},"data":{},"exception":{"name":"ServerException","specificType":"System.IO.IOException","message":"The process cannot access the file 'C:\\Windows\\TEMP\\image.jpg' because it is being used by another process."}}