>Can the following be a factor?
>
>When I create the field, I create it with the DEFAULT WITH VALUES syntax. But, when I need to enlarge its column, I am creating a temporary field without those clauses because I do an update to replace all the fields of the temporary fields with the original field values and renaming it after.
>
>

>   IF NOT EXISTS (SELECT * FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = 'MyTable' AND COLUMN_NAME = 'FirstName')
>      BEGIN
>         SET @Command = N'ALTER TABLE [MyTable] ADD [FirstName] char(25) DEFAULT '''' WITH VALUES'
>         EXEC sp_executesql @Command
>      END
>      ELSE
>      BEGIN
>         SET @Command = N'ALTER TABLE [MyTable] ADD [FirstName-Temporary] char(25)'
>         EXEC sp_executesql @Command
>         SET @Command = N'UPDATE [MyTable] SET [FirstName-Temporary]=FirstName'
>         EXEC sp_executesql @Command
>         SET @Command = N'ALTER TABLE [MyTable] DROP COLUMN [FirstName]'
>         EXEC sp_executesql @Command
>         EXEC sp_RENAME 'MyTable.FirstName-Temporary', 'FirstName' , 'COLUMN'
>      END
>

>
>This never fails when the field does not exist. But, when it exists, I am using the alternative route in order to avoid a timeout. On some isolated situations, when the table is big, this is when I have a problem.

May be we need to add some wait in between each command. The else case looks OK to me except that I would not risk using - Temporary and rather use _Temporary as prefix. - requires using of [] and I'm not 100% sure about your last sp_rename command. So, just to be 100% safe I'd change - to _

Also, could it be a problem with case-sensitive collation of the Server? In that case all field names should match exactly how they are defined in the database.