Why Can't I Use the Eraser in Illustrator?
Adobe Illustrator's Eraser tool offers an intuitive way to remove parts of your artwork as you design and refine it. It simplifies the tasks of editing Illustrator files by removing the need to select individual anchor points or path segments and delete them, and then rejoin open path segments to reshape objects. If you're attempting to revise the elements in an Illustrator file but can't use the Eraser tool on the objects you need to edit, make sure you aren't trying to apply the tool where its functionality isn't accessible.
The Adobe Illustrator Eraser tool can't edit live type. If you want to delete an entire type object, select it with the Selection tool and press the "Delete" key. To remove individual characters from a type object, use the Type tool to select them so you can delete them. Because you can't use the Eraser tool on live type, select it with the Selection tool and convert it to outlines so it becomes vector material.
The Adobe Illustrator Eraser tool has no effect whatsoever on Illustrator's Symbols. If you try to edit what looks like a regular Illustrator object but can't use the Eraser tool to alter it, open the Symbols panel and make sure your object isn't a Symbol. If it is, you must click on the Break Link to Symbol button in the Symbols panel, thereby expanding the Symbol's appearance, in order to edit it using the Eraser tool.
When you place vector artwork into an Adobe Illustrator document and choose to bring it into your file as a linked object, you can't edit the graphic using the Eraser tool. Your only option is to open the original file in Illustrator and apply the Eraser tool in that document itself. On the other hand, if you place vector artwork and embed it into your file, you can use the Eraser tool to edit your graphic because embedded art becomes part of the file into which it's embedded.
Raster Effects and Placed Bitmaps
If you place or paste bitmapped artwork into an Adobe Illustrator file, you can't edit these graphics with Illustrator's Eraser tool because the Eraser tool operates only on vector material. To apply eraser functionality on a bitmap you want to use in Illustrator, open the original file in Adobe Photoshop and alter it there. While you can edit a vector object with the Eraser tool, you can't use the tool to edit any raster effects you've applied to the object, although the effects' appearance may change if you reshape the object with the Eraser tool.