Rahul,

>Is there any rule that the command has to be less than 255 character or
>what can be the reason.

Yes, the index expression is limited to 240 characters or less for CDX-type indexes. You may also be running into problems if your "contact1" field is a memo field or if your expression evaluates to a zero-length result on the first record indexed.

You'll find the information you need in the help files (INDEX Command).