Are you compiling and exporting your assembly from NinjaTrader?
If yes, then you probably had to set up References for your other indicator dlls. When you export, NT will give you a warning that the dlls need to be present on any other target system where you attempt to import the package. The created zip file will include a AdditionalReferences.txt file in it. You will need to manually remove this file. Then you have to include the dll for your indicators into the zip file manually.
If you add the individual indicator dlls, it is going to cause multiple interactions during import which isn’t as clean as having a single combined assembly.
A better way would be to combine the dll from export with dll(s) of your indicator(s). There are various tools to do this. If you use AgileDotNet, you can combine the various assemblies into a single assembly using it. In my opinion, this is the cleanest method and creates a single combined dll which you can include in your zip file.
If you have AgileDotNet, take a look at my post below where I explained in detail how to do this.
Hope this addresses your question.