This problem can only happened when several computations have been done in the worksheet. In other words, the situation could not be reproduced, if the variable and formula are assigned manually. Here is a piece of code that can produce the error. bug.mw

The first block of code produce the Error. The next blocks are trying to identify the error. Please pay attention to the last two blocks which I showed in my first post, where I used the same command: fsolve.

Thank you for your effort and reply that show me a great way to check the solutions. But my problem is still there. What would you think the reason is for what I got in my first statement?

Thank you for your effort and reply that show me a great way to check the solutions. But my problem is still there. What would you think the reason is for what I got in my first statement?