A_MSSQL_MAX_COLUMNS indicates the maximum number of columns allows in a table. The default value is 1024.
Microsoft SQL Server places a limit on the number of columns per table. adheres to this limit, but sometimes it cannot accurately count how many columns a table contains (because a column has been added to a table without knowledge). This variable enables the developer to set upper bound. You might want to try reducing the upper bound if you discover that a table cannot be created. By reducing the upper bound, you allow for uncountable columns and thus may be able to prevent this problem.
If Microsoft SQL Server increases the maximum number of columns allowed per table (in a future release of the product), you could increase the value of this variable to take advantage of the new limit. Consult your Microsoft SQL Server documentation to decide the new maximum number of columns allowed per table.