Western Digital USB Hard disk not working properly on windows 7 build 7057

Hi All,

I have installed Windows 7 build 7057 on my desktop.There is an problem with my external hard disk(Western Digital 160GB).
Before the drive was formatted and partitioned in to 4 parts and I am having data on all drives.On WIndows 7 I am able to see the first partition .

Through disk management I am able to see even remaining partitions of the drive but I am not able to assign drive letter. While assinging drive letter an error alert is coming.

Please find the attachement.

Please provide a solution to get rid of this problem.

Thanks
Madhu

I found the problem for my external hard disk.The problem is due to wrong partitioning.Bfore I partitioned my hard disk in to four primary partitions.Yesterday, I re- partitioned my hard disk in to one primary and other to extended partitions.