Generally said, you can do it.

You must take care that the "inner" protector does not CRC check the file (at least not in an other way than the normal PE-checksum) or else the protected file won't run.

Next you must take care with the IAT protection. The "outside" protector can only protect those APIs, which the "inner" protector imports. It might happen that both protectors like to hook the same API for protection reasons and make the program crash this way.

Then you must know what protector protects what section and what kind of data types. You should choose it in such a way, that in the final executable all sections are encrypted.

If you take an older, not so advanced protector or only an executable compressor and wrap it with an advanced protector, you should not run into much or any trouble. But this way you might lower the protection of the advanced protector, since it can't modify the original code, data and imports with any of it's "traps".

So generally said: Two protectors on the same file are possible, but you should rethink if it's advisable to use both, since they may lower each other's protection.