**Mixing versions is a bad thing!** Running new scripts (12.6x) in old PC environments (12..57 or lower) is not supported. You will encounter issues just like yours and more.
Scripts created in VuGen 12.60 **WILL NOT work properly** in LR 12.55 OR PC 12.55 nor will it work in 12.56 or 12.57 or any lower versions. There are many updates to the TruClient code in VuGen 12.60, which PC 12.55 CANNOT handle. The biggest change being the supported Firefox (TruClient browser) and Chrome (Chromium) versions being used within the TruClient protocol for LR and PC.
**In LR/PC 12.55 the TruClient version of are:**
- Firefox 40.03
- Chrome - Chromium 55
- Internet Explorer 10, 11
**In LR/PC 12.60-12.63 The TruClient version of are:**
- TruClient browser - Equivalent to Firefox version 58.0.2
- Chrome - Chromium 63 (12.60 & 12.61) Chromium 68 (12.62 & 12.63)
- Internet Explorer 10, 11
**HIGHLY Recommend you upgrade ALL machines in your PC environment and All VuGen machines to same and newest version!**
Older scripts (i.e. 12.53) will work in Newer environments (i.e. LR 12.63 or PC 12.63), in most cases.