Deletion of values in Intial column

I need to delete certain products un consumed forecast in Initial period in SNP. I created a macro to zero out the fcst in Initial period. I am getting ABAP 4 Processor Error. ASSERTION_FAILED. Using the same macro, I could able to zero out future periods. In the macro config if I select past in the step node, I am getting above error. I checked these OSS messages 901957/1036880/1067414, they are not related to my problem. I tried to release Zero forecast for history period, just to zero out the fcst. I am not able to do it. Any body comes across this kind of problem. Any help is greatly appreciated. What is the best way to delete un consumed forecast.