1.19 - conversion issue?

[fireball_xl5]

Hello. I've just upgraded to Windows 64-bit 1.19 (can't remember what the previous version was, but I've not done an upgrade for a while) and tried to convert some books from epub to mobi (something that I've done successfully on numerous occasions with earlier versions). The conversion failed - on the Jobs page, the 'Status' stayed at 'waiting' and the 'Progress' stayed at 'unavailable'. I tried with both a batch of books and a single book, with the same results. I then uninstalled 1.19 and installed 1.17 - this time, the conversions worked successfully. I've left 1.17 in place. Is there an issue with 1.19, or was it just 'one of those things'? Thanks.