When you create a project with Laz trunk (not fixes, not 2.0.10) its xml files are written in the new structure with non-numbered nodes which IIRC was required for better maintanance in version control. When you open this project in a non-trunk version the project appears to be empty and it cannot be compiled - yes, without an error message.
You can fix the issue when you open the project again in Laz trunk, go to "Project Options" > "Miscellaneous" and check the box "Maximize compatibility of project files (LPI and LPS)". When you save the project files are rewritten with the old numbered nodes, and non-trunk Laz versions can read it.
If you are a component writer you will be faced with the same issue regarding packages. But there is also a "Maximize compatibility" checkbox in the package options which must be set in the same way. Please note that until several months ago there was bug in this feature which erased the "Maximize compatibility" checkbox from time to time. Therefore, it is highly recommended to use a more recent trunk version.
If you do not use trunk your own projects will not be affected. Only when you open projects written by other people which use trunk. Since you don't have trunk you're out of luck... Contact the author of this project and ask him to set the compatibility flag.
Of course if somebody wants to be a hero for the Lazarus community he could write a conversion tool which reads the new xml files (lpi, lps, lpi), finds the non-numbered nodes, renames them with numbers (<file1> instead of <file>) and rewrites the files. And to become a super-hero you could write an IDE extension which could be installed into older versions.