As long as most of the projects are not implemented according to the approved time schedule , which of these is the weakness point : the management software used, failure of the team management, or illogical signed contracts ?

failure of the team management, 

As per my view majority of projects are delayed due to improper FEED,Un-professional and illogical Contracts that are forced to signed by L1 Contractor.In minor cases projects may get delayed due to Failure in management team and Corruption in higher management.

of all the three choices, the most likely reason would be "failure of the team management" followed by "illogical signed contracts". team management covers so much area like materials, manpower, equipment logistics, supervision, planning and scheduling and more that any delay or error committed (in planning and scheduling) in these would surely affect your completion time unless recognized and rectified as soon as possible.

Thanks for the invite, I agree with the rest of experts answers

I would say it is a failure of Project Management/Team Management !

Thank You

The reasons for delay in project implementation could be for several reason as follows: 

1.    Inaccurate estimate of time (illogical signed contract)

2.    Delay in recruitment of key personnel

3.    Delay in procurement due to some approval process or for bid review

4.    Inaccurate scheduling of activities and time estimate for dependent activities.

5.    Lack of team motivation and work sprit (Failure in Team Management)

6.    Not the management software itself but not using the software rationally thereby resulting in lack of management control  system. 

 It is hard to define a weakest point but certainly the failure is due to all i.e. sum of all weakest points

thanks for invition ...............i agree with previous answers 

agree with expert answers above

(i)Optimistic & unrealistic time schedules

(ii) Environmental or ecological factors

(iii) Power shortages

(iv) Strikes or lockouts

(v) Frequent changes in project scope

Thank you for your invitation and opportunity to share my view. There are many reasons for the failure of project. The main causes are listed below.

1. Poor Planning/In-adequate planning & scheduling
2. Change in Scope
3. Ineffective Management i.e Project Manager
4. The non-support form Higher Management
5. Delay in funding
6. Improper Risk Analysis
7. Poor Productivity of Resources
8. Budget
9. Lack of Materials
10. Poor Communication
11. Involvement of Stakeholders

Agree with Eng. Mushriq abdul majeed Answer