Flash Builder 4.5 the import could not be found

Question

I just upgraded from Flash Builder 4 to 4.5 and have imported  one of my FB 4 projects.  I am now seeing an orange question mark in  the gutter next to all of my import statements that are importing local  classes (as well as everywhere the said class methods are used) and an  orange underline appears under the import statement.  When I hover over  the underline it says that the import could not be found. 
The class files do in fact exist and the project compiles and runs without a problem (I use ANT to build this project).
If I open one of the class files in question then change something  (i.e press space bar) and hit save then go back to the file importing it  the orange question mark is gone for that import, I get the code assist  and CTL+Click links me to the class file.  However, if I close that  file and reopen it again cannot find the class file.
The classes in question are stored under my project's src dir as:
- src
  +---com
      +---myappname
          +---services
          +---utils
          etc...
and my import statements look like:
import com.myappname.utils.*;
import com.myappname.services.remoteService;
Any ideas?  Is this a FB 4.5 "enhancement"?  I've tried deleting and  re-importing the project, refreshing the project and am now kind of at a  loss of what to do.  It's annoying enough that I may need to downgrade  to 4.

Answer 1

Thanks for the reply srvikram13, I really appreciate it.
Unfortunately this did not solve my problem.  The application was developed in Flex sdk 4.1 and I have installed the 4.1 sdk and told the Flex Compiler to use that specific sdk to no avail (I even re-tried per your post, but no success).  The fact is that the project compiles fine with either 4.1 or 4.5 sdk, it just has issues finding the imorted classes until I manually open the class files.
Further debugging and info:
I actually thought I had it fixed for a second.  I renamed my "com" directory and right clicked on "src" and chose "New" > "Package" then repeated that for each directory under "com".  I then closed FB and in windows explorer copied my original com directories into the new one created by FB.  When I launched FB and opened the main file all my imports were recognized!  I then closed FB and re-opened again to see if it was truly fixed and ... epic fail.  The squiggly underlines are back and FB doesn't recognize any reference to them.
I also found that even if I navigate to the class files in the Package Explorer then right click on the file and choose properties, then click cancel (never opening or changing anything) the reference to that specific file is now valid... at least until I close and reopen FB.
Any other ideas?