Recently migrated from SBS2003 to SBS2011, now WinXP clients are extremely slow when browsing mapped drives. Win7 and server 08R2 RDP server access is fine. It is extremely noticeable when adding attachments to outlook via the paperclip (2-3 minute delay). "Drag & Drop" in outlook does NOT experience this slowdown. Also noticeable when uploading items to web-based app.
Turning off SMB2, disabling all "advanced" network functions on NIC, applying latest service packs, clearing mapped drives out of registry, and lots of other things.
Problem affects any user profile on client pc.