"I am using C51 dos based compiler"

Many vendors call their 8051 cross-compilers "C51" - which one do you have?
what version?
how old is it?

Is it a "full" product, or a free demo/evaluation?
Free versions very often do have limitations on code size etc - check the documentation.

"I am using 64k memory for code."

I assume you mean that your target has 64K code memory?
Do you need to configure something in your compiler to tell it that you've got that much? Perhaps it is assuming a (much) smaller default?

"The error is displaying while compiling the c51 file itself."

The error message should give line number (and probably also character position) at which the problem was detected.
Where precisely is it detecting the error?

As I said before, the Manual and/or online help should have a section giving more detailed explanations of the error messages - what does your Manual say about this error?

"I would like to store some l00 names in code memory. How can I?"

What you're doing should work - you need to go through the questions above to try and find out why it doesn't