Synaptic 包管理器失败并显示以下错误：
W: There is no public key available for the following key IDs:
1397BC53640DB551
W: Failed to fetch http://dl.google.com/linux/chrome/deb/dists/stable/Release
Unable to find expected entry 'main/binary-i386/Packages' in Release file (Wrong sources.list entry or malformed file)
E: Some index files failed to download. They have been ignored, or old ones used instead.
Synaptic 包管理器：
E: The value 'trusty' is invalid for APT::Default-Release as such a release is not available in the sources
E: _cache->open() failed, please report.
我该如何纠正这个问题？