Calling up the machine language monitor on the VIC20

[Holbi1]

With the FE3 module, calling the machine language monitor from the VIC20 with SYS24576 only sometimes succeeds. I switched off the ROM area of ​​the monitor with +BLKD 1.3. The machine language module works from (hex)6000. My assembler program starts at (Hex)A000. The program itself works perfectly. What can be the reason?

[ops]

What makes you think it is firmware issue?

[Holbi1]

@ops BLKD . ......... This command disables one or more memory blocks. The disabled blocks are
physically removed, like not existent. Disabled blocks can be used by other cartridges. After the BLKD command one or more numbers are entered separated by commas. Possible values are 0, 1, 2, 3 or 5 (block numbers). If that doesn't work, what should be the problem other than the firmware?