Hi Raju,
As suggested earlier by so many people, please replace where equnr IN it_tab1-equnr with WHERE equnr = it_tab1-equnr.
If you look at your internal table there will be only one EQUNR in each row of that internal table. IN operator is used for RANGES, but when considering a single row of the internal table EQUNR is single value, not a RANGE. So, you can't use IN operator for that.
Hope this solves and clarifies your query.
Thanks,
Anubhab