Schedule:

Unrealistic schedules. to develop a huge software in a single day.

Client:

Ambiguous requirements definition, requirement and not clear, changes in the requirement etc.

Human Resources:

Non-availability of sufficient resources with the skill level expected in the project.

System Resources:

Non-availability of procuring all critical computer resources either hardware and software tools or licenses for software will have an adverse impact.

Quality:

Compound factors like lack of resources along with a tight delivery schedule and frequent changes to requirements will have an impact on the quality of the product tested.