I want to say at once that this problem takes place in Mambo sites of the third level.
I have already written about the slowing the problem with ways while using the third level domain in Mambo sites in one of my previous articles. I have written in those article that it is undesirable to enter the domain of the third level in the variable $mosConfig_live_site. If you still want to enter the address of your site kind of http://mambo.your_mambo_site.com in variable $mosConfig_live_site in the file configuration.php and using visual editor FCK Editor, the problem may be while adding image or link in those editor.
We often need to add image or link in the text which we edit. And mambot moismage is not always the best decision. That is why we use help of the cool editor which allows not only to add image but also to complement it with different virtues, which are not accessible in moismage usage.
To my mind, one of the best editors is FCK Editor. But it also has some defects.
As you remember we are talking about the site situated under the domain of the third level.
When you press the button “Insert Edit the image” dialogue window “image properties ” opens on the tools panel of the editor.
Here you can enter URL address of the image you need, or you can use the button “look on the server”. It is more convenient both, when the image is downloaded on the server and when it is needed to be downloaded (which is very useful function of this editor and replaces usage of Media Manager).
After the pressing of the button “look at the server” you will see the window of the integrated file manager (Resources Browser). With the help of those manager you can choose any image from the directory \images ore one of the subdirectories, you can also create new folder and load the image on the server.
After you have chosen the image you need, you are back to the window “image properties ”, where the chosen image should be reflected in the preview window. The way to the image on a server is indicated in an address line, and in the fields «width» and «height» - its sizes.
 Absence of image in preview window can be the signal of alarm, where in place of it you can behold a little red cross reporting that a way to the image is indicated incorrectly.
After a look at the way to the image you will see that instead of the way for example
http://mambo.your_mambo_site.com/images/stories/food/milk.jpg there written a way http://www.your_mambo_site.commambo.your_mambo_site.com/images/stories/food/milk.jpg, which is incorrect. However deleting the part of the line  www.your_mambo_site.com, you will get the right way to the image in the preview window, but the fields “width” and “height” will be empty and you will not be able to change parameters of the image with saving of proportions. Better to say, proportions will be saved, but not in relation to the real sizes of your image, but in relation to the sizes of those red cross, I.e. 28х30 pixels.

Similar problem takes place in adding the links to the image. May be somebody will decide that it is possible to leave it. But for those, who wants to use all the possibilities of this editor for fullest, there is rather simple way out.
Set a variable value $mosConfig_live_site = http://www.your_mambo_site.com/mambo, but not http://mambo.your_mambo_site.com in configuration file configuration.php
Now use the way http://www.your_mambo_site.com/mambo/administrator to enter admin-panel of your site.
Read about the way out of the problem with ways during the usage of the third level domain on Mambo-sites in the other article.