There are many possible causes for this issue, and it may be hard to resolve. Please take whichever of the following steps is applicable that you haven't already tried. Back up all data before making any changes.
If you get the alert in the login screen before you log in, stop here and ask for instructions.
Step 1
If you get the alert as soon as you log in, it's probably caused by one of your login items or by software that otherwise loads at startup or login. Common offenders are "1Password" and "Adobe Resource Synchronizer," but there are many others.
Select the Login Items tab in the Users & Groups pane of System Preferences. Delete any suspicious items. If you're not sure which ones to delete, double-click each to test it.
To avoid confusion, note that checking or unchecking the box next to a login item does not inactivate it. You have to delete the item from the list.
Step 2
If there's an icon representing the server in the sidebar of a Finder window, hold down the command key and drag it out.
Step 3
You may have created aliases to files or folders on the server. If you don't know whether you did that, you can find all aliases as follows.
Triple-click anywhere in the line of text below on this page to select it:
kMDItemContentType=com.apple.alias-file
Copy the selected text to the Clipboard by pressing the key combination command-C.
In the Finder, press command-F to open a search window, or select
File ▹ Find
from the menu bar. In the search window, select
Search: This Mac
from the row of tokens below the toolbar. Below that is a popup menu of search criteria, initially showing Kind. From that menu, select
Other...
A sheet will drop down. In that sheet, select
Raw Query
as the criterion, then click OK or press return.
Now there will be a text box to the right of the menu of search criteria. That's where you enter the raw search query. Click in that box and paste the text you copied earlier by pressing command-V.
The search window will now show all aliases on mounted volumes. You can see the target of each alias by selecting it and opening the Info window. Delete any that refer to the server.
Step 4
Open the Printers & Scanners pane in System Preferences and delete any network devices you no longer use. If in doubt, delete them all and add back the ones you want.
Step 5
Copy the line below to the Clipboard as in Step 3:
~/Library/PDF Services
In the Finder, select
Go ▹ Go to Folder...
from the menu bar and paste into the box that opens. You won't see what you pasted because a line break is included. Press return. A folder may open. If it does, move the contents to the Desktop, or to a new folder on the Desktop. Log out and log back in. Test. If there's no change, put the items you moved back where they were and continue.
Step 6
Open the folder
~/Library/Preferences
as in Step 5 and move the file named "loginwindow.plist" items in that folder to the Trash, if it exists (it may not.)
Log out and back in again, and test.
Step 7
Other possible causes are references in the iPhoto, iTunes, or iMovie library pointing to the server, bookmarks in the Preview application, and PDF files created by Adobe Acrobat with embedded scripts.
Try rebuilding the iPhoto library, if applicable.
If you get the alert when connecting an iOS device with iTunes, re-create your iTunes library and playlists. See also this discussion.
Step 8
Resources such as images or sounds stored on the server may have been added to various applications. Examples would be pictures added to Contacts and custom sounds added to Mail. The range of possibilites here is practically infinite, so I can't be more specific. You might get a hint by launching the Console application and looking for error messages that appear at the same time as the alerts.
Step 9
Disconnect all wired peripherals except those needed to start up. Start up in safe mode. Test. After testing, restart as usual (not in safe mode) and verify that you still have the problem.
Note: If FileVault is enabled in OS X 10.9 or earlier, or if a firmware password is set, or if the startup volume is a Fusion Drive or a software RAID, you can’t do this. Ask for further instructions.
Step 10
Launch the Directory Utility application. Depending on what version of OS X you have, you may be able to do that by entering the first few letters of its name in a Spotlight search. If that doesn't work, triple-click anywhere in the line of text below on this page to select it:
/System/Library/CoreServices
Right-click or control-click the selected text and select
Services ▹ Open
from the contextual menu.* A folder named "CoreServices" will open. The Directory Utility application is in that folder, or in a subfolder named "Applications".
In the Directory Utility window, select the Directory Editor tool in the toolbar. Select Mounts from the Viewing menu in the toolbar, and /Local/Default from the node menu, if not already selected. On the right is a list of names and values. By default, the list is empty. If it's not empty, post a screenshot of the window and stop here.
*If you don't see the contextual menu item, copy the selected text to the Clipboard (command-C). Open a TextEdit window and paste into it (command-V). Select the line you just pasted and continue as above.
Step 11
Open the following file as you did in the last step:
/etc/auto_master
It will open in a TextEdit window. The contents should be exactly this:
#
# Automounter master map
#
+auto_master # Use directory service
/net -hosts -nobrowse,hidefromfinder,nosuid
/home auto_home -nobrowse,hidefromfinder
/Network/Servers -fstab
/- -static
If there are any other lines in the window, post them. Otherwise, close the window.
