Are you trying to open a project with the xml extension in BAS? Probably your project is damaged, you did not edit it manually using text editors? Try to restore it from backups located here:
C:\Users\User\AppData\Roaming\BrowserAutomationStudio\projectbackups
@battalcengizhan
Do you use fingerprints and proxies?
What version of BAS are you using?
At what point does the error occur (registration, authorization, posting)?
It would be cool to write everything according to this instruction: https://community.bablosoft.com/topic/30993
