Eagle project wont open, "Error reading file"
If it is a recent Eagle version, you may open the .brd and .sch files with a text viewer, because they are basically xml text files. This may give you a clue of what is happening or a way to fix it. 

BTW, eagle also keeps a few backups (exact number is configurable) of the last saves. 

For example, .sch backups will look like this:

mysch.s#1
mysch.s#2
...


Similary, .brd backups will look like this:

mybrd.b#1
mybrd.b#2


And even library backups (previous saves) will look as follows:

mylbr.l#1
mylbr.l#2
...