Reserved words in SharePoint url

Avoid using these words in any SharePoint url (file name, folder name, site name etc.):

CON, PRN, AUX, NUL, COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8, COM9, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, LPT9

You can create folder named “CON”, but when you go to folder url, you get 404 error.

Thanks to the following articles:
http://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx
http://spcz.blogspot.com/2012/03/sharepoint-reserved-words.html

How to initialize PeopleEditor control?

You can use CommaSeparatedAccounts property for users. But this property doesn’t work for groups.

SPGroup

PeopleEditor peopleEditor = ...;
SPGroup group = ...;
PickerEntity entity = new PickerEntity
{
    Key = group.LoginName,
    DisplayText = group.Name,
    Description = group.Name,
    IsResolved = true
};
entity.EntityData.Add("AccountName", group.LoginName);
entity.EntityData.Add("SPGroupID", group.ID.ToString());
entity.EntityData.Add("PrincipalType", "SharePointGroup");
peopleEditor.Add(entity);

SPUser

PeopleEditor peopleEditor = ...;
SPUser user = ...;
PickerEntity entity = new PickerEntity
{
    Key = user.LoginName,
    DisplayText = user.Name,
    Description = user.Name,
    IsResolved = true
};
entity.EntityData.Add("AccountName", user.LoginName);
entity.EntityData.Add("SPUserID", user.ID.ToString());
if (user.IsDomainGroup)
    entity.EntityData.Add("PrincipalType", "SecurityGroup");
else
    entity.EntityData.Add("PrincipalType", "User");
peopleEditor.Add(entity);

How to handle version conflict during Update operation

You can use Microsoft.Office.Server.Utilities.EventReceiverUtility class and IsVersionConflictException method. You can find it useful when you use SPWeb.AllProperties for some application counter for example.

SPWeb web = ...;
bool retry = true;
int count = 0;
while (retry)
{
    try
    {
        int lastId = 0
        if (web.AllProperties.ContainsKey("LastId"))
            lastId = (int)web.GetProperty("LastId");
        else
            web.AddProperty("LastId", lastId);

        lastId++;
        web.SetProperty("LastId", lastId);
        retry = false;
    }
    catch (Exception ex)
    {
        if (!EventReceiverUtility.IsVersionConflictException(ex))
            throw;
        if (count > 2)
            throw;
    }
    count++;
}