You need to be a site collection administrator to set this property.

Issue Description

Recently I was trying to add a site collection administrator to a site and I got the belowmessage

You need to be a site collection administrator to set this property.   at Microsoft.SharePoint.ApplicationPages.ManageSiteAdminPage.BtnSubmit_Click(Object sender, EventArgs e)

   at System.Web.UI.WebControls.Button.OnClick(EventArgs e)

   at System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument)

   at System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument)

   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

I was already the site collection administrator to the site and it did not make any sense.

Fix

On further trouble shooting, I found the solution for this.Browse to Central Administration - > Site Collection Quotas and Locks.

The options available here are:

       Not locked

Adding content prevented

Read-only (blocks additions, updates, and deletions)

No access

This site collection was in Read-only status. Unlock it (Change the status to  "Not Locked")

Setsitelock: Stsadm operation

Sets a value that specifies whether the site collection is locked and unavailable for read or write access. This operation should be used in conjunction with the Getsitelock operation. For more information, see the Examples section.

Syntax

stsadm -o setsitelock

   -url <URL name>

   -lock {none | noadditions | readonly | noaccess}

None: Sets the site collection to unlock.

Noadditions: Permits changes that reduce the size of the data.

For example, if you had an announcement list item whose body consisted of 50 characters, you could successfully edit the list item so that the body was reduced to 25 characters. However, if you tried to edit the list item so that they body was increased to 100 characters, that would be blocked.

Readonly: Sets the site collection to read-only.

Noaccess: Sets the site collection unavailable to all users.

Examples

To determine the lock status of the site, you can use the following getsitelock syntax:

stsadm -o getsitelock -url http://server_name

Once the lock status of the site collection is determined, you can use the noaccess parameter of the setsitelock operation to lock out all users to the site:

stsadm -o setsitelock -url http://server_name -lock noaccess

Reference

How to Unlock a site collection manually

1. Browse to SharePoint Central Administration.

2. On the Central Administration page, under Application Management, click Configure quotas and locks.

3. On the Site Collection Quotas and Locks page, select the site collection where you want to place a lock

4. In the Site Lock Information section, select Not Locked.

5. Click OK.

How to Lock a site collection manually

1. Browse to SharePoint Central Administration.

2. On the Central Administration page, under Application Management, click Configure quotas and locks.

3. On the Site Collection Quotas and Locks page, select the site collection where you want to place a lock

4. In the Site Lock Information section, select Adding content prevented or No access.

5. If you lock a site collection with Adding content prevented or No access, you must type an explanation in the Additional lock information box.

6. Click OK.