I just received a circuit from another user and when I go into transient analysis and try to run, I get an error stating that Micro-Cap can't find a .TOP file.
The .TOP file is created by the State Variables Editor and is used to store the State Variables that initialize the start of the transient simulation. You would need to get this file from the other user, or in the Transient Analysis Limits, you can change the State Variables option to Zero or Leave. When this option is set to Read, there must be a corresponding .TOP file present.
Note that if you change the State Variables option to Zero or Leave, you will most likely receive a different simulation than the other user due to the different initial conditions.