@tomleslie 

Thank you very much for your response and help!

The program runs now without obstacle. 

There was zero cases which verifies all of the the conditions I impose. When I remove the condition  

if   (ai>aineg)
then f*(aineg-ai)=0

I get 2621 cases which are good.

Thank you very much for your response.

But it is weird. I keep receiving the original error message, and not the one you mention.

(p) is the solution of Equation (eqp). So normally (p) is assigned. In the "if" command, I ask to give me positive values of (p)...

@Carl Love 

Thank you very much for your help Carl! My program works perfectly now!

Do not worry, I will not print all these iterations :)

Kind regards,

Basak

Thank you very much for your quick and detailed answer.

This is super helphul!

Thank you very much.

Kind regards

@Preben Alsholm 

Hi,

I am sorry. My program was incomplete when I have copied it. The correct beginning of the program is:

som:=0;

tot:=0;

N:=10;
for a from 4000 to 5000 by 100 do
for b from 100 to 900 by 10 do
for c from 3000 to 3000 by 100 do 
for d from 3000 to 3100 by 10 do
for e from 10000 to 10000 by 100 do
for f from 600 to 700 by 10 do
for p from 1 to 10 by 1 do
tot:=tot+1;
 

Thank you!

@Kitonum 

Thank you very much for your help!

Best regards.

@acer 

Thank you very much for your help!

Best regards.

@_Maxim_ 

Thank you very much Maxim for your elegant solution! Even though I understand nothing on the details of the command, it works perfectly well!

Thank you again.

Best regards