Can you attach a code snippet that generates the error? This check is done in the discrete time portion of the code and so a small error between dt and sys.dt should not really occur (the only allowed differences between dt and sys.dt should be specifying a simulation sample time that is an integer multiple of the system sampling time).

Also, can you indicate which version of python-control you are using (control.__version__ will tell you). The line that you indicated doesn't seem to match the latest release.

My "control" version is 0.8.2, Python version 3.7.3 (IPython 7.6.1) Windows 10 (64 bits)
The problem can be demonstrated by a simple test:

import numpy as np
samp_rate = 500e3
T = np.arange(100)
T[1]-T[0]
Out[5]: 2e-06

T[2]-T[1]
Out[6]: 2e-06

T[3]-T[2]
Out[7]: 2.0000000000000003e-06

T[4]-T[3]
Out[8]: 1.9999999999999995e-06

So, if we call timeresp.py with T[3:] as our time steps in simulation, line 265 "dt = T[1] - T[0]" will yield dt = 1.9999999999999995e-06, but sys.dt should be 2e-6. Subsequently, line 337 will raise the ValueError.

If simulation time uses T, or T[1:], or T[2:] will have no problem!

It seems the problem goes away by changing line 337 in timeresp.py to:
if abs(dt - sys.dt) > 1e-18:

Thanks for the extra info @bj2sn. A fix will be a bit more complicated because the discrete time simulation routines allow you to specify a sample time for the simulation that is a multiple of the sampling time for the system. So, for example, you can have that dt is 2 * sys.dt. On the current master, this check is done on line 362.

Will put this on my list of things to fix.

Fixed in PR #356.