Is Microsoft Dynamics CRM 2011 roll up 12 is Supporting .net 4.5 Framework.Will there be issue with Plugin workflows.
Yes, after roll up 8, MSCRM 2011 currently supports .Net 4.5 for plugin development.
Microsoft Dynamics CRM Compatibility List
Product | Minimum CRM Version | CRM Build Number | Status
.Net Framework 4.0 | RTM | 5.0.9688.583 | Compatible
.Net Framework 4.0 | PU3 | | TBD
.Net Framework 4.5 | Update Rollup 8 | 5.0.9690.2243 | Compatible