Question : Formula/Cunction Needed

As always I've turned to Experts Exchange for my difficult/challenging problems and I appreciate your solutions. Today i Need an IF statement/formula that will give me a count or ID based on the number of occurances that exact string appears. Let me try to explain The formula should be in Column B and it should give the results below: Notice if the string only appears once like 100101*01 then it should be blank, only if the string appears more than once it should start to number them 1,2,3,4 etc.
Column A   Column B  
100101*01
100202*01  1
100202*01  2
100202*01  3
100203*01  1
100203*01  2
100204*01
100205*01
100206*01  1
100206*01  2
100206*01  3
100206*01  4

If you have any other questions please let me know and i really appreciate your time trying to figure this out.

Answer : Formula/Cunction Needed

my mistake again....

This formula should work for you.

=IF(COUNTIF(A:A,A1)=1,"",COUNTIF($A$1:A1,A1))

let me know. sorry for the confusion.