If you are using the version meant for your os..
If you have got all your dependencies ...
And they are checked and meant for the version you need...
And app man is telling you that the dependencies that need to be satisfied cannot be installed because they are ALL "incompatible packages" ...
And since the version and its dependencies hasn't changed over at least 3 770 os iterations including Gregale that you are using, it is doubtful ...though possible you got a dependency that should be for a different version...
But if you are sure you were exacting and omitted nothing ...

then there is something wrong here that you have overlooked or omitted in the process.
It must be.
Installing xterm is one of the first and most fundamental installs to be able to access the system, and shouldn't be a problem on a clean reflashed system.
Since you then have no known or unknown problems impeding.

It is a clean reflashed fresh 770 you are working on... right?
Otherwise ...
God only knows where the problem(s) is(are) springing from...and what mess you are inheriting from someone else or from forgetting what one has done to said device years and years ago..