The IRS uses Notice CP102 to tell you that they believe there is a mistake on your tax return. This is essentially the same as the various Forms CP11, etc., sent to Individuals. The process is much the same, too, But, businesses carry an extra burden because the IRS can impose enormous penalties which can cripple a business.
Respond to Notice CP102
Therefore, it is important to investigate this adjustment. You'll need to review the actual filed return to determine if it is correct. Review the IRS notice carefully for the full explanation of the changes. Check your payments to see if they were made timely. If everything appears correct, you may have to involve the Taxpayer Advocate. You only have 60 days to respond within the IRS administrative system.
Often, the IRS records are not wrong, they just lack the information necessary to offset or diminish the tax. You will probably have to gather some evidence and you may have to file an amended return. In this example, Form 941-X.