does table names have a format and size

Hi,

Is the name of the table important in psql... because the following
create table command doesn't create any table in the database but the
next sql command with a different table name creates the table.

Is there any table name convention in postgres.

create table IL18R---_PGA_SNPs666 (contig char(10),contig_pos
char(10),read_pos char(10),chromat char(30),sample char(30),allele1
char(20),allele2 char(20),ref_pos char(10),ref_sample char(10),tag
char(100),source char(10));

following command works well...

create table MD1_PGA_SNPs666 (contig char(10),contig_pos
char(10),read_pos char(10),chromat char(30),sample char(30),allele1
char(20),allele2 char(20),ref_pos char(10),ref_sample char(10),tag
char(100),source char(10));

thanks
Prakash