Another way to combine dosage regimens for a single subject : You can try and separate dosage regimens and not to put them together in a single parentheses. Through this, you are clearly defining multiple dosage regimen for a single subject.
And make sure to use same round brackets on combining the dosage regimens. I encountered the same error and square brackets contributed to the error.
A single subject who received a 500 mg IV dose at
time = 0, followed by followed by 100 mg dose at
time = 12 that is given every 12 hours for 5 additional doses
ev1 = DosageRegimen(500, time=0, cmt=2,)
ev2 = DosageRegimen(100, time=12, cmt=1, ii=12, addl=4)
evcombined =DosageRegimen(ev1, ev2)
s1 = Subject(id=1, evs=evcombined, cvs=(isPM=0, wt=50))
obs1 = simobs(yourmodelname, s1, para, obstimes=0:1:120)
This should run your model with combined dosage regimen for a single subject.
Hope this helped!