Backup disk is inaccessible

WD External Drives External Drives for Mac
1

My Book Studio Edition™ II – Time machine backup  is not available now.

It worked fine for two years but some times ago started failed. From yesterday it said no  finally. I had reinstalled WD Drive Manage and reboot a computer but t’was in vain.

WD Drive Manage shows My Book is healthy and a Disk Utility the same. I can record a files to My Book but not Time machine backup.

Had anybody the same trouble? What a solution?

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Mac Pro Mid 2010, OS X 10.8.2 (12C60), WD Drive Manager v3.0.1.

2

how much available space do you still have?

did the problem started after you upgrade to Mountain Lion?

3

A problem existed in a Lion. It said that disk is damaged then I had restored it in a DiskUtility. For a some time it becomes impossible whithout erasing all data though it never was full. At last I have described situation.

4

Now I use it for storage some documents. Copy/paste is incredible slow.