What are the main kinds of problems which manufacturing companies struggle with?

In addition to all the above mentioned I believe locating new unsaturated markets,proper new market penetration plans,government constant laws and regulation changes,political unrest,resources...etc.

Mr. Mohammed Thiab has explained this Question properly  

QUALITY , SKILLED HUMAN RESOURCE , FAST CHANGING RULES OF MANUFACTURING , LATEST EQUIPMENTS , SECURITY MEASURES ,  ISO RESTRICTIONS.

Agree with Ahmed Sharab.

Labour

Raw Material

Planning

Dispatch

Delivery

1) To meet the customer requirement 

2) Timely Delivery

3) Manufacturing Cost should not exceed our budget

1- Finding customers

2- productivity

3 - reject

4- down times

Agree with Mr. Mohammed Thiab

Its production, opreations & logistics

1. Market pressure for higher quality products at lower  and cmore competitive costs
2. Staying ahead of the others in innovation and creativity in products and production itself
3. Supply chain optimization to ensure avaiability of parts/components/assembiies  just-in-time with minimal dead stocks
4. Automation and optimization of the production/assembly line itself to maximize throughput and ease the handling of inputs and outputs
5. People dimension in terms of skills, competencies, ... and how to to maintain and grow them

Manpower.

Product quality.

Mismatch between production and sales projection.