Windows 7 Server Busy Error

Just a longshot but if you have google toolbar or ask or anything like that installed try getting rid of it. I've seen those toolbars do strange things with attachment functions.

The 'server busy' message is appearing because the program is trying to access the internet before the connection is completely ready.

It sounds like you have installed programs configured to access the internet and perform an operation, such as check for updates for that program.

To check which program is trying to update using the internet I would suggest that you perform clean boot procedure and check.

Here is how you can do clean boot for windows 7:
 
Otherwise I suggest you to install and run Ccleaner and clean unnecessary files from  your hard drive and registry. Its faster and easier way:

You can download ccleaner from here

Good luck

Are you using Exchange? if so what version?
Pop3 Imap?
How large are the PDF files?

IS it just PDF files or all attachments?

I ran CCleaner, did a clean boot, uninstalled toolbars and still issue persists?

Maybe this will be more clear.  The end-user is using a scanner Fujitsu ScanSnap S510, scans a document and attaches the pdf to the email.  It is at that point the Server Busy error appears...???

If the file is saved to the desktop then there is no issue, only when attaching to an email.

Is this a 64 bit version of windows 7?
Is outlook 64 bit?

I see the scanner offers 64 bit drivers

Ok, I will try updating the drivers for the scanner.

You are absolutely correct.... compatability issues persist...  

http://www.fujitsu.com/global/support/computing/peripheral/scanners/ssfaq/office2010.html