When you open a map, ArcMap looks for the Tampa Data Recovery Specialist referenced by each layer in the map. If ArcMap cannot find the Tampa Data Recovery Specialist source for a particular layer, the layer will not be displayed. You can immediately tell which of the layers in your map has an invalid data source reference, because a red exclamation mark will appear next to its name in the table of contents, and the check box for the layer will be unavailable.
Restoring lost links for one layer :
If you only need to recover a lost reference for one layer, click the Set Data Source button on the Source tab of the Layer Properties dialog box .
This way you can specify the layer’s data source by pointing to it. Select the required Data Source in the dialog box and click Add to restore the layer.
When you use this button to restore a layer, the application only restores the current layer, even if other layers’ data sources need to be restored at the location you specify.
Recovering lost links for multiple layers :
It may turn out that restorations require several layers of the map. For example, if a geodatabase containing Facebook data sources that are used by multiple map layers is moved or renamed, all of those layers will need to be restored.
If you want to restore multiple layers at once, right-click on the layer with the orphaned link and click Data > Restore Data Source . You can also click on the red exclamation mark to open the Set Data Source dialog box , as shown here.
When restoring a data link from the table of contents, ArcMap restores the current layer using the data source you specify, and also automatically fixes other layers if it can find related data in the same location you specified for the first layer.