Infinity result in Measure to Calculated column

Thanks for coming back to me! 

We are calculating the percentage of contacts against transactions.  We have 115,180 contacts and 7,891,981 transactions.

So we count the items in the contact and transaction columns:

Count of Contacts = COUNT('MASTER MERGE'[CaseNumber])

Count of Transactions = COUNT(Transactions[RA_Number])

We then calculate the percentage:

% Contacts v Transactions = COUNT('MASTER MERGE'[CaseNumber])/COUNT(Transactions[RA_Number])

There are 67 case resolution types associated with each contact.  When we add the case resolution type for the contacts in chart form, the model provides a percentage of contacts for that resolution type against the number of transactions.   It works perfectly except for one of the case resolution types.  It occurs only once in the contact data set and gives a result of infinity.  What is really strange is that another resolution type occurs only twice, yet gives a correct result.