When ComEd bungled the launch of a new computer billing system in February, it left millions of customers unable to see their balances or pay online for more than a week before it was ostensibly resolved. But for thousands of ComEd customers participating in the state’s community solar program, the billing debacle continues. For nearly four months, subscribers to community solar farms dotting the landscape across northern Illinois have been unable to get credit for the power generated to offset their regular ComEd bills.