This is the single most overlooked cause. If your RAM has a single bad bit, Unarc.dll will throw Error -7 consistently. The installer works fine for small programs but fails on large compressed archives.
Guided Fixes (ranked by safety)
Open (search for sysdm.cpl in the Run box). Go to Advanced > Performance Settings > Advanced tab. Under Virtual Memory , click Change . Uncheck "Automatically manage paging file size". isdonedll error unarcdll error7 best
Corrupted data in your temporary folders can interfere with new installations. Open , type %temp% , and press Enter. This is the single most overlooked cause
Go to under the Performance section, then the Advanced tab. Under Virtual Memory , click Change . Guided Fixes (ranked by safety) Open (search for sysdm
Keep every folder name as short as possible (e.g., "GTA5" instead of "Grand Theft Auto V – Ultimate Edition").