When a layout .jt file is imported in Robcad, the generated .co file is incomplete(size of .atr and .gri files are 0KB) and thus not able to load component in Robcad (using "Get component"). The TxJt2co translator shows successful translation of .jt file to .co file and the .jt file is clearly visible in Vis Mockup.
Due to the fact, that JT2CO works in general, the JT-file might be the cause.
You may try converting it to a monolithic JT and import again.
But probably the forum is not the right place to help in this case.
I suggest to open an IR at GTAC and attach your JT to it.