Currently Google Drive is incompatible with calibre. Calibre uses numbers in parenthesis in its folder structure to identify books. Here is an example:
John Carter's Chronicles of Mars (1907)
When this folder is moved to Google Drive the (1907) may be removed and certainly will be modified at some point. Without this identifier calibre library will not function. Google uses numbers in parenthesis for version control. You can read this
discussion in the Google Drive discussion group that outlines the problem. This issue was first posted in May 2012 and as yet has not been fixed.
Until further notice do not put your calibre library in your Google Drive space.
Update: If your library has been damaged by moving the library to Google drive then there are two possible solutions created by folks here at Mobileread.
1. This solution uses .Net/Windows and was created by
Mattes,
read this post.
2. This solution uses a Python script and was created by
mendhak. This solution has been tested on Ubuntu 14.04, but may work for other OSes as well,
read this post.