I get that when the vector has gradient fills from ID or occasionally with grouped objects. I usually have no problems if I use Object>Transform>Scale, or type in the scale value. It's just the click and drag that seems to have problems.

You should save your artwork as an Illustrator .ai file then import using File > Place. Because you pasted the artwork is not treated as one single graphic but as a group of native InDesign objects. Small objects and details are being scaled down until the details are beyond InDesign’s ability to distinguish individual details.

I just got this error (and found this post by searching google), when creating a little, simple (fewer than 20 points) vector shape directly within InDesign (CS5.5, Mac) using the Pen tool.

I created the shape, and then tried to shrink it down ~50% to fit into the space I'm needing it to fit inside. At first, it did something I've never seen before: I clicked the corner, held down Shift to lock the aspect, and then started to drag. The preview outline box shows me what I expect (an outline getting smaller), but when I let go, the shape returns back to the previous size and location.

Feeling confused and frustrated by this, I then tried to use the actual "size" dialogs within the quick toolbar or whatever that contextual thing on top is called. That's when I get the "Requested value is not a legal dimension" error. I looked at my shape very closely, and there is nothing special about it at all. The shape itself is over 2 inches wide, composed of two separate lines. I need it to be just over 1 inch wide. Strangely, when I turn it into a compound path, the error goes away. It doesn't look like the excuse given for this behavior in this thread really holds up under testing.

Just the standard Selection tool (V).

Peter, I know you're trying to help, but my method of tool selection/usage is not an issue. I have been using InDesign on a Mac every weekday since v. 2.0 came out and I switched from QXP 3.3. I use keyboard shortcuts like most people use forks and spoons. Maybe I didn't describe what I did properly because I am so used to the keyboard shortcuts that I'm not even aware of everything I'm doing. I had the frame selected, and I was resizing both the frame and the content proportionally when the "snap-back" error occurred. You're right that I was holding down command in addition to shift. I only mentioned shift to indicate that I was resizing proportionally. As a test, I just tried putting the vector object group into a separate rectangular frame and resizing it that way, both by selecting the vector shapes of the group, and by selecting the frame. I am unable to resize the contents of the frame irregardless of which way I do it. I have uploaded the object to my Dropbox account for you to look at it.  http://dl.dropbox.com/u/20763863/error_sample.indd.zip

Had the exact same problem, Ben. For me, it was a grouped ID line drawing. I was able to shrink by ungrouping, but that's not the answer I was looking for. Instead, changing a preference did the trick: In Preferences, General, I check "Adjust Scaling Percentage." Hope that works for you.