The PM have to be a technical expert on the subject of the project?

And @Diego, perhaps you have to take advantage that there are people participating here I always that I always read their comments because the level of knowledge they have. I will do that (hehehehe). If we ask the question what does means to be a technical expert as project manager?. If we take the definition or the PMBOK Guide when the BOK talked about techniques are techniques you can find inside and are related to project management. But when you search the job request those techniques are related to software (for example SQL, Oracle DB, etc) or network or hardware. So, organizations that post this type of request are searching subject matter experts that, as an additional duty, will try to lead the team that are creating the product/service/result. Then they are not searching for a project manager.

A project manager is a professional in the field of project management. Project managers oversee the project to ensure the desired result is achieved, the most efficient resources are used and the different interests involved are satisfied.
Though if he has remained involved in a specific industry, he might have a better insight of that industry and it would give him an extra edge.
But in general he doesn't necessarily needs to be a technical expert in the industry for whom he is managing project.

All good points supporting my view that it helps to know the 'language' of the industry sector snd be able to talk to and understand the subject matter expert. It is not necessary to be the subject matter expert

I will agree with my colleagues here. The PM should have a basic understanding of the software but anything deeper than that, should be addressed by the technical lead. The PM will get more comfortable and will understands more about the product with every project he is leading.