when short cuts are used to move from one open file to another I get an error message, "Unable to complete command due to low system resources"
 
With only three files open and setting the shortcut o CTRL SHFT 1/2/3/4 etc for each file, then executing CTRL SHFT 4 results in the above error message.  
 
Perhaps this feature should be trapped so that either a proper error message is displayed or nothing happens.
 
 
Albert