Siemens In InOut and Out in FBs

In Step 7, does anyone one if there is a problem with using a variable declared as in the OUT area of FB interface as an input within the logic of the FB itself? Sometimes the program will not let me and sometimes it will. Do I need to change all data that will be used somewhere on the input side of the FB logic to InOut?

Thanks

If its only internal in the fb make it a stat
If you need it outside of the call make it an input output

For example, I have several Outputs for different failures: Fail_to_start, Fail_to_stop, Limit_switch_fail.
I write the failure data to these three bits then later in the FB I read from them to assign the data to a general failure bit. Step 7 has allowed this, but in other occasions, it does not allow me to read from an output at all.

IN_OUT's are only critical in FC's.

In FB's all parameters except TEMP's are held in the IDB, therefore an output state is remembered internally.