Searching a string in eclipse workspace

At the top level menus, select 'Search' -> 'File Search' Then near the bottom (in the scope) there is a choice to select the entire workspace.

For your "File search has encountered a problem", you need to refresh the files in your workspace, in the Project/Package Explorer, right click and select "Refresh" at any level (project, folder, file). This will sync your workspace with the underlying file system and prevent the problem.

Press Ctrl + H, should bring up the search that will include options to search via project, directory, etc.

Ctrl + Alt + G can be used to find selected text across a workspace in eclipse.