Have you tried my formula?? It is working here!! In case you want to substitue my formula in the one that is present in column 2 it should be like this:
Countif() will take your data as numbers and that is giving problem in your case, SUMPRODUCT() takes data as "Text" and that will work here, It will check if the cell contains the same text as you have mentioned to count for, will retrun true or false for each case, this true/false multiplied by 1 will give you 1 for every true and when sumproduct will sum, you will get the count of certain thing.
thanks Faseeh,I tried it,but i have a question,so here i have to write it as =IF(SUMPRODUCT([column1]=[column2])*1)>1,1,0) right? since Im writing the formula in column 2 ,it gives me circular reference error also. ????