When running the Mailbox size report you can see the error below.
Unexpected error while attempting to read from the database.
Timeout expired
SELECT [Display Name] AS S0, [Date] AS X0,SUM([Mailbox Size (KB)]) AS Y0 FROM (SELECT [Display Name], [Date], SUM([Mailbox Size (KB)]) AS [Mailbox Size (KB)], [Organization], [Server],
[Site/Administrative Group], [Region], [Last Logon Date], [Hidden], [Messages Stored],
[Server Store Distinguished Name], [Department], [Company], [NTAccount], [Title], [Office], [Assistant],
[Phone], [Address], [City], [State/Province], [Code], [Country], [Last Name], [First Name], [Initials],
[Custom Attribute 1], [Custom Attribute 2], [Custom Attribute 3], [Custom Attribute 4], [Custom Attribute 5],
[Custom Attribute 6], [Custom Attribute 7], [Custom Attribute 8], [Custom Attribute 9], [Custom Attribute 10],
[Custom Attribute 11],[Custom Attribute 12],[Custom Attribute 13],[Custom Attribute 14],[Custom Attribute 15],
[Creation Date], [Warning Quota (KB)], [Send Quota (KB)], [Receive Quota (KB)], [Container/Organizational Unit],
[NT Account Domain Version], [Alias], [Date Last Modified], [X400 Address], [Associated NT Account Type], [Disabled],
[Mailbox DN], [Mailbox Email], [Storage Limits], [Gathering Status], [Server Roles], [Routing Group], [Last Mail Received],
[Last Mail Sent], [Last Logged On By], SIPAddress, [Storage Group]
FROM (SELECT *, dbo.FU_ServerRoles(ServerGUID, 'en-US') AS [Server Roles] FROM V_MailboxSizePerUser) ServerRolesQuery
WHERE [Display Name] IN
(SELECT TOP 10 [Display Name]
FROM (SELECT *, dbo.FU_ServerRoles(ServerGUID, 'en-US') AS [Server Roles] FROM V_MailboxSizePerUser) ServerRolesQuery WHERE ((([Date] >= '2011-01-09' AND [Date] < '2011-01-16') AND [Site/Administrative Group] = N'FIRST ADMINISTRATIVE GROUP' AND [Organization] = N'Serigraph'))
GROUP BY [Display Name]