Impact of check digit algorithm value in EAN category

Hi All ,

I have an EAN category VC (Velocity code (int. assignment possible)).

It has an internal and external number range assignment.

A.The current external number range assignment is as following

000000000000000001 - 000000000000499999.

B. The requirement is to change this number range as given below-

100000000000000000 - 49999999999999999.

Also the Check digit algorithm value maintained is 1(Standard EAN check digit algorithm).

But when I am changing the number range as per my requirement( as per point B) , the system gives an error message

"The EAN 100000000000000002 may not be assigned externally"

When i make the check digit algorithm field value blank , the system does not give the error message.

Please let me know the relationship between check digit algorithm value and number range assignment of EAN category.

Thanks.