Whenever git user/password authentication is used on Windows agent will not be able to successfully authenticate. The best workaround is to switch to ssh authentication or update to newer version.

Workaround

• Stop Bamboo 6.3.0
• Replace atlassian-bamboo-plugin-git-6.3.0.jar with attached atlassian-bamboo-plugin-git-6.3.0-BAM-19587.jar at BAMBOO_INSTALL/atlassian-bamboo/WEB-INF/atlassian-bundled-plugins
• Replace atlassian-bamboo-api-6.3.0.jar with attached atlassian-bamboo-api-6.3.0-BAM-19587.jar at BAMBOO_INSTALL/atlassian-bamboo/WEB-INF/lib
• Start Bamboo 6.3.0
  Remote agents will download upgraded jars on next reconnect