I've worked with Ldt 2007 version 2009 but I've installed it, my problem is not that previous versions of files to open in 2009 and I continue to work with Ldt do the same in 2007.
Is there any way I can solve this problem?
If you are asking about working an old file in 09, and then trying to go back to 07, then the answer is it's very difficult to do, and you will wind up recreating most of the work.
ACAD products have never really been backwards compatable and it's especially true for the verticles like LDC/LDT & C3d. Your best bet is to port a project up to the newer versionm and keep it there. If there are others in the office or clients that need the older version, keep it in that version. Don't try to bounce back & forth - it doesn't work.
The only way I really know to back track a project is with XML files, and that causes problems in itself, because not everything can go via XML.