Why did owncloud stop syncing?

Question

Data synchronization

Worth owncloud 2.1.0
Windows 7 64bit
Unexpectedly stopped synchronizing files, the red cross is on, writes access denied.
At random, I realized that if you change the properties of the folder into which owncloud is synchronized and remove the read-only checkbox, it synchronizes once, and then the red cross starts to burn again and you need to repeat everything with the folder all over again
. What is this and how to fix it?