Hi, thanks for the quick response. I think I worded my OP badly. I meant I have only had experience with Vault, and I'm unfamiliar with Design Assistant. The files I'm working with haven't been used in Vault and were generated by my client in an old version of Inventor, so I'm using the same version. So when I looked into migration it didn't seem to apply to my situation, i.e. same versions of Inventor.
But I tried a simple test assembly with just two parts in Design Assistant and it functioned correctly. So I knew there was a problem with my clients assembly. I went back to DA and opened the assembly and that's when I noticed the warning messages when I loaded it (that I'd previously ignored!). There were two parts that were created in even older versions of Inventor. Then I realised that they might be the issue and sure enough when I checked the file details they were created in Inventor 2011! So I looked into migration again and discovered Task Scheduler. Migrated the files and then everything worked in Design Assistant. It never would have occured to me that just 2 parts in an assembly of over 50 parts would prevent me from performing any action in Design Assistant.
So all is good and I discovered how to use two new useful programs that I'd never used before. (I didn't know I could batch create STEP files using Task Scheduler either). Thanks for your help.
