Please help to write correct code.

I neet add custom field GroupProgram into Group Profile

1. I add this field into system table Community_Group class Community.Group throw CMS Site Manager / Development / System tables
2. After in file ~\CMSModules\Groups\Controls\GroupEdit.ascx I add new custom field and add code into SaveData() class

------------------------
if (group != null)
{
if (this.DisplayAdvanceOptions)
{
// Update Group fields
group.GroupDisplayName = displayName;
group.GroupName = codeName;
group.GroupNodeGUID = ValidationHelper.GetGuid(this.groupPageURLElem.Value, Guid.Empty);
}

if ((AllowChangeGroupDisplayName) && (IsLiveSite))
{
group.GroupDisplayName = displayName;
}

group.GroupDescription = this.txtDescription.Text;
group.GroupProgram = this.txtProgram.Text;
group.GroupAccess = GetGroupAccess();
group.GroupSiteID = this.SiteID;
group.GroupApproveMembers = GetGroupApproveMembers();
group.GroupSendJoinLeaveNotification = this.chkJoinLeave.Checked;
group.GroupSendWaitingForApprovalNotification = this.chkWaitingForApproval.Checked;
this.groupPictureEdit.UpdateGroupPicture(group);

---------------

But error accured

Compiler Error Message: CS1061: "CMS.Community.GroupInfo" does not contain a definition for "GroupProgram". and no extension method "GroupProgram", accepting a first argument of type "CMS.Community.GroupInfo" could be found (are you missing a using directive or an assembly reference?)

Source Error:

Line 342:
Line 343: group.GroupDescription = this.txtDescription.Text;
Line 344: group.GroupProgram = this.txtProgram.Text;
Line 345: group.GroupAccess = GetGroupAccess();
Line 346: group.GroupSiteID = this.SiteID;


Source File: c:\inetpub\KenticoCMS\CMSModules\Groups\Controls\groupedit.ascx.cs Line: 344

How can I solve this error?

Version of Kentico v5.5.4125 R2