Unable to modify table.

I was trying to modify a table of approx 5 million records setting a field on the table to not allow null values. However, while saving changes in table, I got below error:

'Account ' table
- Unable to modify table. 
Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding.

After that I click ok button and I got below error:

User cancelled out of save dialog.

This error is coming because table designer have a default timeout value of 30 secs. And as I am saving a table with huge records, it is taking time more than 30 secs, so above error coming.

So the solution is to increase the timeout value of designer, (the maximum value for timeout is 65535).
Click on tools menu - Options - Expand designers. Now here change the timeout value in "Table and Database designers" on the right side.

Unable to modify table.

We were trying to modify a table of approx 5 million records setting a field on the table to not allow null values . we received the following error on SQL Server 2008 R2 Management Studio when we tried to save the changes made on the table.

'Customer ' table
- Unable to modify table.
Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding.

When we clicked on the OK button, we received a second error.

The main cause of the problem is Table designer have a default time out value of 30 seconds. Since saving the modifications made on the table was taking more than 30 seconds then we received the error message.

The solution is :

Let’s increased the time out value to 65,535, the maximum value.

We clicked on the Tools menu, then clicked on “Options”, and clicked on “Designers” on the left panel. After that, we changed the value in the “Transaction time-out after:” textbox.