If my employer mistakenly changed my filing status to single for part of the year, how does that affect my taxes?

If your withholding was Single, no dependents, your employer withheld the maximum amount.  Depending on your return, you may receive a bigger refund,  

Thanks. That is what I would have assumed. However, as soon as I plugged my W2 in all of a sudden I owe $6000 on a salary of about $48,000 and almost $5000 was already taken out during the year. 

@knl0422  If that $48K is the only income that you have then there is a problem with how you entered the K-1.  

If you have a lot more income that your 48K is added to then it can be taxed at a much higher rate than is with held by the employer.  Employers only withhold on the income that they pay you.  They don't know that your tax rate is much higher because of a bunch more investments or your spouse's salary.