All else being equal, I would meet first with your supervisor to get his/her view of yur duties and your relationship with the team and its members, particularly the Team Leader (TL). Next meet with the TL to get insight into the project requirements and team organizational issues. Also you will need to get clarity of your respective roles before involving the rest of the team. You don't want to upset your TL with a public misinterpretation of your roles or upset your team with a open disagreement with your TL.
Most employers would expect you, the Project Manager (PM), to understand the policies, processes, and practices that the development team employs but not necessarily to be proficient in the technology being implemented. However some employers will expect the PM to additionally perform as a subject matter expert or developer; this can put you in the awkward position of balancing your role as a PM with executing work packages.
Did you employer hire you knowing your LAMP experience and that this was a .net application? If yes to both, they should be understanding your dilemma and let you be the PM, not a part-time PM and part-time developer.
Not being experienced with .net may be a blessing in disguise. As a former web developer you may be tempted to roll-up-your-sleeves and pitch into the work - at the cost of doing your job as a PM. At the project schedule slips and/or costs rise, you may become stressed and revert to a role you are more comfortable with: web developer. Resist this temptation. Otherwise you will leave the project without a steady hand at the wheel.
For a project of any magnitude, they will be numerous stakeholders to manage; you will have your hands full keeping them happy - or at least pacified. For more on stakeholder management, see my answer at Working with a "single point of contact". In addition, the PM needs to be vigilant for scope creep, resource attrition, team morale, change control, and a thousand other concerns aside from the tech being developed.