"Confess your faults one to another, and pray one for another, that ye may be healed. The effectual fervent prayer of a righteous man availeth much. James 5:16"
The opening scripture above is dealing with corporate prayer, which can be applied to prayer in general. Failure to forgive hinders corporate prayer; no wonder Apostle James said we should be bold enough to tell one another where we or they are going wrong so that corporate prayer can be a time of feasting and refreshing because answers are received and miracles, signs, and wonders are pronounced.
As a child of God, you should not keep offence inside you as it will pollute your spirit. Go to the offender quickly and show him/her his/her fault quickly and politely before it begins to harm you. The enemy would want you to keep offence inside you so that he can rely on it to destroy your conscience and spiritual growth in prayer.
Don't allow him; put him to shame and enjoy prayer any time you pray alone, and especially church/corporate prayer meetings. Praise the Lord!