Proc Report requires that you use a specific type of variable reference for analysis variables in your COMPUTE block.
So, for example, if I wanted to divide height by age in this program:
proc report data=sashelp.class nowd;
column name age height divided;
define name / order;
define age / sum;
define height / sum;
define divided / computed;
divided = height.sum / age.sum;
To make this work, I have to give DIVIDED (my new report item) a usage of "COMPUTED". Then, I need a compute block for divided. Since I defined AGE and HEIGHT as analysis variables with a usage of 'SUM', then I need to ALSO use their "compound names" in the COMPUTE block for DIVIDED. Those compound names are: varname.statistic
which means age.sum and height.sum need to be used in the compute block.
So you were -almost- there try this:
if Coveragecode = 'MC' then Frequency = Claimcount.sum / EarnedCov.sum;